Calculation sequence
Step-by-step method
- Confirm the measurement boundary, time basis, and formula symbols.
- Apply the displayed equation to the user-entered values.
- Review data quality, uncertainty, project criteria, and professional disposition.
CommissioningIntermediateTrend Analysis
Three-Point Trend-Slope Calculator
Calculate the least-squares slope for three equally spaced values and the fitted middle value.
Why it matters: Transparent data reduction keeps raw values, criteria, symbols, and arithmetic available for review.
Calculated result
Engineering evaluation
Three-point least-squares trend slope (m)1.2 units/min
- Fitted value at middle sample (b)
- 15.667 units
Engineering interpretation
The equally spaced three-point trend changes at 1.2 units/min.
Important limitations
- Data-reduction screen only. Project requirements, test procedure, instrument uncertainty, sampling, and authorized engineering judgment remain controlling.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
For t=[0,Δt,2Δt], m=(X_3−X_1)/(2Δt)
b=X̄
displayed symbols: X_2
Current substitution
m=(22−10)/(2×5)=1.2; b=15.66667.
Equation legend
Inputs and calculated quantities
- X_1
- First sample — selected units
- X_2
- Second sample — selected units
- X_3
- Third sample — selected units
- Δt
- Sample interval — min
- m
- Three-point least-squares trend slope — units/min
- b
- Fitted value at middle sample — units
Applications
How this calculation is used
Building design
Prepare a visible analytical basis for a planned test or monitoring point.
Construction
Reduce startup, TAB, controls, and field-observation data consistently.
Commissioning
Evaluate recorded measurements without hiding project criteria or uncertainty assumptions.
Quality controls
Assumptions and limitations
Assumptions
- Entered observations describe a common measurement boundary and compatible units.
- Sampling, timestamps, instruments, and user-entered criteria are documented outside the arithmetic.
Limitations
- The calculation does not create an acceptance criterion, uncertainty budget, or engineering disposition.
- Project requirements, procedures, calibration, data quality, and authorized judgment remain controlling.
Field use
Verification procedure
- Confirm the test boundary, sampling interval, units, and raw-data source.
- Enter the recorded values and any authorized user-supplied criterion.
- Review the arithmetic with uncertainty, procedure, and project requirements before disposition.
Common engineering mistakes
- Combining unsynchronized values or incompatible measurement boundaries.
- Ignoring resolution, uncertainty, sample selection, missing data, clock offset, or test conditions.
Technical basis
References and source standards
- NIST Measurement and SI ResourcesMeasurement traceability, units, and uncertainty context.
- ASHRAE Guideline 0 and Commissioning ResourcesCommissioning-process and verification context; project requirements remain controlling.
- AABC Commissioning GroupCommissioning practice and field-verification context.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement