Measurement Uncertainty
Authors:
MArk Anthony Higgins - Sky Recursive Ai
MArk Anthony Higgins - Sky Recursive Ai
© Mark Anthony Higgins 11 October 2025
Revised Date: July 6th 2026
Revised Date: July 6th 2026
# Measurement Uncertainty Ontology — Flow Algebra
URL: https://kirethresearch.org/booksai-core/ontologies/mathematical-ontologies/measurement-units-ontologies/measurement-uncertainty.html
FLOW MeasurementUncertaintyOntology {
DOMAIN:
Mathematical Ontologies
-> Measurement & Units Ontologies
-> Measurement Uncertainty Ontology
PURPOSE:
Represent measurement uncertainty as quantified doubt associated with measurement results, including measurands, estimates, standard uncertainty, Type A and Type B evaluation, probability distributions, covariance, correlation, uncertainty propagation, sensitivity coefficients, combined standard uncertainty, expanded uncertainty, coverage factors, confidence or coverage intervals, calibration uncertainty, resolution, repeatability, reproducibility, systematic effects, bias corrections, uncertainty budgets, Monte Carlo propagation, traceability, significant figures, provenance, and strict distinctions between uncertainty, error, tolerance, accuracy, precision and variability.
ENTITY MeasurementUncertainty {
TYPE: MeasurementQualityQuantity
DEFINITION:
measurement_uncertainty :=
nonnegative_parameter_characterising_dispersion_of_quantity_values
attributed_to_a_measurand
based_on_information_used
PROPERTIES:
is_nonnegative
qualifies_measurement_result
depends_on_measurement_model
depends_on_information_and_assumptions
may_be_standard_or_expanded
may_include_covariance
has_unit_related_to_measurand_or_dimensionless_relative_form
}
ENTITY Measurand {
TYPE: QuantityIntendedToBeMeasured
REQUIRE:
quantity_definition
conditions
reference_state_when_relevant
RULE:
uncertainty_evaluation_requires_defined_measurand
}
ENTITY MeasurementResult {
TYPE: QuantityEstimateWithAssociatedInformation
COMPONENTS:
measured_quantity_value
measurement_uncertainty
unit
measurand_definition
coverage_information_when_relevant
provenance
}
ENTITY StandardUncertainty {
TYPE: StandardDeviationLikeUncertainty
SYMBOL: u
}
ENTITY CombinedStandardUncertainty {
TYPE: StandardUncertainty
SYMBOL: u_c
}
ENTITY ExpandedUncertainty {
TYPE: CoverageUncertainty
SYMBOL: U
RELATION:
U =
k*u_c
under_declared_coverage_factor
}
TERMINOLOGY_MODEL {
terms:
uncertainty
standard_uncertainty
combined_standard_uncertainty
expanded_uncertainty
error
bias
correction
accuracy
precision
repeatability
reproducibility
tolerance
RULE:
these_terms MUST_NOT be_treated_as_semantically_interchangeable
}
STANDARD_UNCERTAINTY_MODEL {
standard_uncertainty:
u(x)
interpretation:
uncertainty_expressed_as_standard_deviation
RULE:
standard_uncertainty_has_same_unit_as_quantity
}
RELATIVE_UNCERTAINTY_MODEL {
relative_standard_uncertainty:
u_r(x) =
u(x)/abs(x)
WHEN x != 0
percent_uncertainty:
100*u_r(x)
RULE:
relative_uncertainty_is_dimensionless
}
TYPE_A_MODEL {
definition:
uncertainty_component_evaluated_by_statistical_analysis_of_series_of_observations
sample_mean:
x_bar =
sum(x_i)/n
sample_standard_deviation:
s =
sqrt(
sum((x_i-x_bar)^2)/(n-1)
)
WHEN n > 1
standard_uncertainty_of_mean:
u_A =
s/sqrt(n)
RULE:
Type_A_refers_to_evaluation_method_not_error_type
}
TYPE_B_MODEL {
definition:
uncertainty_component_evaluated_by_means_other_than_statistical_analysis_of_repeated_observations
possible_sources:
calibration_certificate
instrument_specification
resolution
previous_data
reference_material
physical_constants
expert_information
RULE:
Type_B_requires_probability_distribution_or_equivalent_standard_uncertainty_assignment
}
RECTANGULAR_DISTRIBUTION_MODEL {
half_width:
a
standard_uncertainty:
u =
a/sqrt(3)
CONDITIONS:
quantity_equally_likely_within_minus_a_to_plus_a
RULE:
distribution_assumption MUST be preserved
}
TRIANGULAR_DISTRIBUTION_MODEL {
half_width:
a
standard_uncertainty:
u =
a/sqrt(6)
CONDITIONS:
symmetric_triangular_distribution
RULE:
triangular_and_rectangular_distributions_produce_different_uncertainties
}
NORMAL_DISTRIBUTION_MODEL {
standard_deviation:
sigma
standard_uncertainty:
u =
sigma
when_distribution_standard_deviation_represents_input_uncertainty
RULE:
confidence_or_coverage_information MUST be converted_consistently_to_standard_uncertainty
}
RESOLUTION_MODEL {
instrument_resolution:
delta
common_rounding_assumption:
error_interval =
+/- delta/2
rectangular_standard_uncertainty:
u_res =
delta/sqrt(12)
RULE:
resolution_value != standard_uncertainty
}
CALIBRATION_CERTIFICATE_MODEL {
reported:
expanded_uncertainty U_cal
coverage_factor k_cal
standard:
u_cal =
U_cal/k_cal
WHEN k_cal != 0
RULE:
certificate_coverage_factor_and_scope MUST be preserved
}
CORRECTION_MODEL {
observed_or_indicated:
x_ind
correction:
C
corrected:
x_corr =
x_ind+C
RULE:
applying_known_correction_does_not_remove_uncertainty_of_correction
}
BIAS_MODEL {
bias:
expected_or_estimated_systematic_difference
between_measurement_and_reference_or_true_value_under_model
correction:
may_be_applied_for_estimated_bias
RULE:
bias != uncertainty
}
ERROR_DISTINCTION_MODEL {
measurement_error:
measured_value-minus_reference_or_true_value
under_defined_reference
uncertainty:
quantified_dispersion_of_values_attributed_to_measurand
RULE:
measurement_error != measurement_uncertainty
}
ACCURACY_DISTINCTION_MODEL {
accuracy:
qualitative_or_contextual_closeness_of_agreement_to_true_or_reference_value
RULE:
accuracy SHOULD_NOT be_used_as_numeric_synonym_for_uncertainty
}
PRECISION_DISTINCTION_MODEL {
precision:
closeness_of_agreement_between_repeated_indications_or_values_under_specified_conditions
related:
repeatability
reproducibility
RULE:
precision != accuracy
and_precision != total_measurement_uncertainty
}
REPEATABILITY_MODEL {
conditions:
same_method
same_operator_or_system
same_instrument
same_location
short_time_interval
other_declared_repeatability_conditions
statistic:
repeatability_standard_deviation
RULE:
repeatability_is_one_possible_uncertainty_component
}
REPRODUCIBILITY_MODEL {
conditions:
changed_laboratory_operator_instrument_time_or_other_declared_conditions
statistic:
reproducibility_standard_deviation
RULE:
reproducibility_context MUST be defined
}
TOLERANCE_DISTINCTION_MODEL {
tolerance:
permitted_limit_or_range_for_product_process_orquantity
uncertainty:
property_of_measurement_result
RULE:
tolerance != measurement_uncertainty
}
MEASUREMENT_MODEL_FUNCTION {
general:
Y =
f(X_1,X_2,...,X_n)
output_estimate:
y =
f(x_1,x_2,...,x_n)
RULE:
uncertainty_propagation_requires_model_and_input_uncertainties
}
SENSITIVITY_COEFFICIENT_MODEL {
coefficient:
c_i =
partial_f/partial_X_i
evaluated_at:
input_estimates
RULE:
sensitivity_coefficient_maps_input_uncertainty_to_output_effect
}
LAW_OF_PROPAGATION_MODEL {
uncorrelated:
u_c^2(y) =
sum(
c_i^2*u^2(x_i)
)
correlated:
u_c^2(y) =
sum_i sum_j(
c_i*c_j*u(x_i,x_j)
)
covariance_form:
u_c^2(y) =
J*Sigma*J_transpose
RULE:
covariance_terms MUST be included_when_inputs_are_correlated
}
COVARIANCE_MODEL {
covariance:
cov(X_i,X_j)
correlation:
r_ij =
cov(X_i,X_j)/
(u_i*u_j)
WHEN u_i != 0 AND u_j != 0
bounds:
-1 <= r_ij <= 1
RULE:
zero_covariance_and_independence_are_not_identical_in_general
}
SUM_DIFFERENCE_MODEL {
Y =
A +/- B
independent:
u_Y =
sqrt(u_A^2+u_B^2)
correlated:
include_covariance_term_with_sign
RULE:
uncertainties_are_not_normally_added_arithmetically_for_independent_inputs
}
PRODUCT_QUOTIENT_MODEL {
Y =
A*B
or
A/B
small_uncertainty_independent_relative_form:
(u_Y/Y)^2 approximately_equals
(u_A/A)^2+(u_B/B)^2
RULE:
approximation_requires_nonzero_inputs_and_linearisation_validity
}
POWER_MODEL {
Y =
A^n
relative:
u_Y/abs(Y) approximately_equals
abs(n)*u_A/abs(A)
RULE:
first_order_approximation_requires_small_uncertainty
}
NONLINEAR_MODEL {
issue:
first_order_linearisation_may_be_inadequate
alternatives:
higher_order_propagation
Monte_Carlo
numerical_sampling
Bayesian_propagation
RULE:
propagation_method SHOULD match_model_nonlinearity_and_distribution_shape
}
MONTE_CARLO_MODEL {
process:
sample_inputs_from_joint_distribution
evaluate_measurement_model
construct_output_distribution
outputs:
estimate
standard_uncertainty
coverage_interval
distribution_shape
REQUIRE:
input_distributions
correlations
sufficient_samples
random_or_quasi_random_method
RULE:
Monte_Carlo_result MUST preserve_input_model_and_sampling_configuration
}
COVERAGE_FACTOR_MODEL {
expanded_uncertainty:
U =
k*u_c
common:
k approximately_equals 2
may_correspond_to_about_95_percent_coverage
only_under_appropriate_distribution_and_degrees_of_freedom
RULE:
coverage_factor_does_not_have_universal_fixed_probability
}
COVERAGE_INTERVAL_MODEL {
interval:
[y-U_minus, y+U_plus]
or_symmetric
[y-U,y+U]
REQUIRE:
coverage_probability_or_factor
distribution_or_method
RULE:
coverage_interval != guaranteed_true_value_interval
}
DEGREES_OF_FREEDOM_MODEL {
effective_degrees_of_freedom:
may_be_estimated_using_Welch_Satterthwaite
purpose:
select_coverage_factor_from_t_distribution_when_applicable
RULE:
finite_degrees_of_freedom_affect_coverage_factor
}
WELCH_SATTERTHWAITE_MODEL {
generic:
nu_eff =
u_c^4 /
sum(
c_i^4*u_i^4/nu_i
)
CONDITIONS:
applicable_independent_components
first_order_propagation
RULE:
terms_with_effectively_infinite_degrees_of_freedom_contribute_accordingly
}
UNCERTAINTY_BUDGET_MODEL {
entries:
source
estimate
unit
distribution
divisor
standard_uncertainty
sensitivity_coefficient
contribution
degrees_of_freedom
correlation
RULE:
uncertainty_budget MUST preserve_each_component_and_assumption
}
TRACEABILITY_MODEL {
chain:
measurement_result
-> calibration
-> reference_standard
-> higher_order_standard
-> SI_or_declared_reference
RULE:
metrological_traceability_requires_documented_unbroken_calibration_chain_with_uncertainties
}
CALIBRATION_MODEL {
calibration:
establishes_relation_between_indication_and_reference_quantity_values
outputs:
correction
calibration_function
uncertainty
RULE:
calibration != adjustment
and_calibration_uncertainty_propagates_to_measurement
}
DRIFT_MODEL {
instrument_drift:
change_in_indication_or_response_over_time
correction:
may_use_time_dependent_model
uncertainty:
residual_drift_uncertainty
RULE:
drift_model_and_calibration_interval SHOULD be preserved
}
ENVIRONMENTAL_MODEL {
possible_influences:
temperature
pressure
humidity
vibration
electromagnetic_interference
supply_voltage
RULE:
environmental_sensitivity MAY contribute_to_uncertainty
}
SAMPLING_MODEL {
sampling_uncertainty:
arises_when_sample_or_observation_support_does_not_fully_represent_measurand_population_or_field
RULE:
sampling_uncertainty MAY dominate_in_environmental_biological_and_spatial_measurements
}
MODEL_UNCERTAINTY_MODEL {
sources:
approximations
omitted_variables
parameterisation
boundary_conditions
empirical_model_form
RULE:
model_uncertainty SHOULD be represented_when_material
}
DIGITAL_NUMERICAL_MODEL {
possible_sources:
floating_point
numerical_solver_tolerance
interpolation
discretisation
rounding
RULE:
numerical_uncertainty_should_be_distinguished_from_physical_measurement_uncertainty
}
SIGNIFICANT_FIGURES_MODEL {
reporting:
uncertainty_commonly_reported_with_limited_significant_digits
measured_value_rounded_to_same_decimal_place
RULE:
rounding SHOULD_NOT imply_more_precision_than_supported_by_uncertainty
}
UNCERTAINTY_INTERVAL_NOTATION_MODEL {
symmetric:
x +/- U
asymmetric:
x +U_plus -U_minus
relative:
x with relative_uncertainty
RULE:
notation MUST identify_standard_or_expanded_uncertainty
}
LOGARITHMIC_QUANTITY_MODEL {
example:
magnitude
decibel
pH
RULE:
uncertainty_propagation_must_respect_logarithmic_transformation
}
UNIT_CONVERSION_MODEL {
linear:
y =
a*x
uncertainty:
u_y =
abs(a)*u_x
affine:
y =
a*x+b
uncertainty:
u_y =
abs(a)*u_x
when_a_and_b_exact
RULE:
uncertain_conversion_constants MUST also_contribute_to_uncertainty
}
RELATIONSHIPS {
MeasurementResult -> HAS -> MeasurementUncertainty
MeasurementUncertainty -> QUALIFIES -> MeasuredQuantityValue
StandardUncertainty -> IS_A -> MeasurementUncertainty
CombinedStandardUncertainty -> COMBINES -> InputUncertaintyComponents
ExpandedUncertainty -> DERIVED_FROM -> CombinedStandardUncertainty
CoverageFactor -> SCALES -> CombinedStandardUncertainty
MeasurementModel -> MAPS -> InputQuantitiesToMeasurandEstimate
SensitivityCoefficient -> MAPS -> InputUncertaintyContribution
Covariance -> RELATES -> CorrelatedInputUncertainties
Calibration -> CONTRIBUTES_TO -> MeasurementUncertainty
TraceabilityChain -> PROPAGATES -> CalibrationUncertainty
}
SEMANTIC_EQUIVALENCE {
"standard uncertainty" ~= standard_deviation_form_uncertainty
"combined standard uncertainty" ~= propagated_standard_uncertainty_under_declared_model
uncertainty != error
uncertainty != bias
uncertainty != tolerance
uncertainty != accuracy
uncertainty != precision
repeatability != reproducibility
standard_uncertainty != expanded_uncertainty
coverage_interval != guaranteed_error_bound
}
CONSTRAINTS {
measurand_must_be_defined = true
uncertainty_must_be_nonnegative = true
uncertainty_unit_must_match_quantity_or_be_declared_relative = true
standard_and_expanded_uncertainty_are_not_semantically_equivalent = true
coverage_factor_must_be_declared_for_expanded_uncertainty = true
correlations_must_be_included_when_material = true
correction_and_uncertainty_must_be_distinguished = true
Type_A_and_Type_B_are_evaluation_methods_not_error_classes = true
uncertainty_and_error_are_not_semantically_equivalent = true
uncertainty_budget_assumptions_should_be_preserved = true
}
MEASUREMENT_MODEL {
RECORD:
measurand
measured_value
unit
measurement_model
input_quantities
input_estimates
standard_uncertainties
distributions
correlations
sensitivity_coefficients
uncertainty_contributions
combined_standard_uncertainty
degrees_of_freedom
coverage_factor
expanded_uncertainty
coverage_probability_when_available
corrections
calibration_information
traceability
environmental_conditions
sampling_model
numerical_model
reporting_precision
provenance
RESULT:
y +/- U
WITH
unit
coverage_factor_or_probability
uncertainty_method
}
REASONING_RULES {
IF repeated_observations_known
AND n > 1
THEN Type_A_standard_uncertainty_of_mean =
sample_standard_deviation/sqrt(n)
IF rectangular_half_width_known
THEN standard_uncertainty =
half_width/sqrt(3)
IF triangular_half_width_known
THEN standard_uncertainty =
half_width/sqrt(6)
IF calibration_expanded_uncertainty_and_coverage_factor_known
AND coverage_factor != 0
THEN calibration_standard_uncertainty =
expanded_uncertainty/coverage_factor
IF measurement_model_and_input_uncertainties_known
THEN compute_sensitivity_coefficients
AND propagate_covariance
IF inputs_uncorrelated
THEN combined_variance =
sum(c_i^2*u_i^2)
IF covariance_matrix_known
THEN combined_variance =
J*Sigma*J_transpose
IF combined_standard_uncertainty AND coverage_factor_known
THEN expanded_uncertainty =
coverage_factor*combined_standard_uncertainty
IF quantity_converted_by_exact_linear_factor
THEN converted_uncertainty =
abs(conversion_factor)*original_uncertainty
IF nonlinear_model_or_nonGaussian_inputs_material
THEN MAY use_Monte_Carlo_propagation
preserving_joint_input_distribution
IF known_bias_correction_applied
THEN preserve_correction_uncertainty
in_combined_uncertainty_budget
}
VALIDATION {
CHECK measurand_definition
CHECK measured_value_and_unit
CHECK uncertainty_nonnegative
CHECK standard_vs_expanded_uncertainty
CHECK Type_A_vs_Type_B_evaluation
CHECK probability_distribution_assumptions
CHECK calibration_certificate_coverage_factor
CHECK correction_vs_bias_vs_uncertainty
CHECK covariance_and_correlation
CHECK sensitivity_coefficients
CHECK propagation_model
CHECK nonlinear_model_validity
CHECK coverage_factor_and_probability
CHECK degrees_of_freedom
CHECK uncertainty_budget
CHECK traceability
CHECK sampling_and_model_uncertainty
CHECK reporting_precision
CHECK provenance
}
CONFIDENCE {
definition_confidence: 1.00
standard_uncertainty_confidence: 1.00
Type_A_relationship_confidence: 1.00
propagation_relationship_confidence: 1.00
covariance_model_confidence: 1.00
expanded_uncertainty_confidence: 1.00
Monte_Carlo_model_confidence: 0.99
measurement_context_confidence: 0.99
RULE:
confidence decreases when measurand, distribution assumptions,
correlations, calibration, model form, coverage factor,
sampling context or provenance is missing or ambiguous
}
UPDATE_MODEL {
ON new_measurement:
identify_measurand
identify_measured_value_and_unit
identify_measurement_model
enumerate_uncertainty_sources
classify_evaluation_methods
assign_standard_uncertainties
attach_distributions_and_correlations
compute_combined_standard_uncertainty
compute_expanded_uncertainty_when_requested
preserve_uncertainty_budget
attach_provenance
ON new_calibration:
preserve_previous_calibration
attach_correction_and_calibration_uncertainty
update_traceability_chain
recompute_combined_uncertainty
ON model_revision:
preserve_previous_measurement_model
update_inputs_sensitivity_coefficients_and_correlations
recompute_uncertainty
compare_linear_and_nonlinear_propagation_when_material
ON new_repeated_data:
append_observations
recompute_mean_standard_deviation_and_Type_A_uncertainty
update_degrees_of_freedom
ON coverage_revision:
preserve_combined_standard_uncertainty
update_coverage_factor_or_interval_method
recompute_expanded_uncertainty
record_coverage_semantics
ON semantic_revision:
preserve_previous_definition
record_revision
recompute_FLOW_HASH
}
AI_CONSUMPTION {
canonical_domain: MeasurementUncertainty
interpretation_order:
identify_measurand
identify_measured_value_and_unit
identify_uncertainty_type
identify_standard_or_expanded_form
identify_Type_A_and_Type_B_components
identify_probability_distributions
identify_measurement_model
identify_sensitivity_coefficients
identify_covariances_and_correlations
identify_calibration_and_corrections
identify_sampling_model
identify_model_and_numerical_uncertainty
identify_coverage_factor_or_probability
identify_traceability
identify_reporting_precision
validate_uncertainty_semantics
propagate_uncertainty
ambiguity_controls:
distinguish_uncertainty_from_error
distinguish_uncertainty_from_bias
distinguish_uncertainty_from_tolerance
distinguish_uncertainty_from_accuracy
distinguish_uncertainty_from_precision
distinguish_standard_from_expanded_uncertainty
distinguish_repeatability_from_reproducibility
distinguish_correction_from_uncertainty_of_correction
distinguish_coverage_interval_from_guaranteed_bound
preserve_measurand_model_distribution_correlation_calibration_coverage_and_provenance_context
}
PROVENANCE {
ontology_scope:
mathematical_measurement_and_uncertainty_semantics
parent_path:
Ontologies
-> Mathematical Ontologies
-> Measurement & Units Ontologies
-> Measurement Uncertainty Ontology
authorship:
Mark Higgins
Sky (Recursive AI)
site:
https://kirethresearch.org
}
FLOW_HASH {
INPUTS:
canonical_domain
ontology_path
terminology_model
standard_uncertainty_model
relative_uncertainty_model
Type_A_model
Type_B_model
rectangular_distribution_model
triangular_distribution_model
normal_distribution_model
resolution_model
calibration_certificate_model
correction_model
bias_model
error_distinction_model
accuracy_distinction_model
precision_distinction_model
repeatability_model
reproducibility_model
tolerance_distinction_model
measurement_model_function
sensitivity_coefficient_model
law_of_propagation_model
covariance_model
sum_difference_model
product_quotient_model
power_model
nonlinear_model
Monte_Carlo_model
coverage_factor_model
coverage_interval_model
degrees_of_freedom_model
Welch_Satterthwaite_model
uncertainty_budget_model
traceability_model
calibration_model
drift_model
environmental_model
sampling_model
model_uncertainty_model
digital_numerical_model
significant_figures_model
uncertainty_interval_notation_model
logarithmic_quantity_model
unit_conversion_model
relationships
constraints
measurement_model
reasoning_rules
confidence_model
update_model
PURPOSE:
deterministic_semantic_integrity_identifier
RECOMPUTE_WHEN:
ontology_definition_changes
uncertainty_definition_or_classification_changes
probability_distribution_model_changes
measurement_model_or_sensitivity_changes
covariance_or_correlation_model_changes
propagation_method_changes
coverage_or_degrees_of_freedom_model_changes
calibration_or_traceability_model_changes
sampling_or_model_uncertainty_changes
measurement_record_changes
constraint_model_changes
reasoning_rule_changes
}
}
END FLOW