Calculations and calibration constants

Calculated variables produce decimal results from equations. They belong to an instrument and can use active decimal variables and calibration constants as inputs.

Create a calculated variable

1. Open the instrument’s Calculated Variables section and create a variable.
2. Give it a name, alias, unit, and expected cadence as needed.
3. Choose One equation for all time or Equations over time.
4. Use Find and insert input to select variables or calibration constants.
5. Build the expression with the inserted input tokens and mathematical operators.
6. Save and follow the recalculation status before checking the result in a graph or table.

Inputs are linked by identity. Use the input picker rather than typing a display label and assuming it will become a reference.

Example: apply a scale and baseline

Suppose a channel contains a raw reading and your measurement procedure defines a scale factor and reference value. Add two calibration constants to the instrument, insert those constants and the raw variable, then construct the conceptual equation:

(raw reading - reference value) * scale factor

Select the actual input tokens in the editor. This illustrates the workflow; choose the equation, constants, and output unit specified for your instrument and monitoring procedure.

Constants retain stable IDs. Editing a constant value can start recalculation for dependent calculated variables, so review the affected variables and resulting run.

Inputs from another instrument

Choose an external variable input to reference an active decimal variable on another instrument in the project. Set Past buffer seconds to control how far back that input may look. Use a buffer appropriate for the source cadence and inspect periods where a source reading is unavailable.

Calculated variables can depend on other calculated variables, but dependencies must remain active and cycle-free.

Equations over time

One equation for all time has one undated calculation. Equations over time supports an optional undated fallback and calculation periods with unique, inclusive start times.

Use periods when the intended equation changes from a known time onward. Review the displayed local date and time carefully and verify values on both sides of the change.

The expression editor supports arithmetic and functions including abs, round, floor, ceil, trigonometric functions, radians, degrees, ln, log2, log10, exp, and sqrt.

Recalculation and history

Creating or changing computation can rebuild historical calculated values. Previous current values remain visible while recalculation runs. If rebuilding fails, the previous values remain visible and the page reports the failure; they should not be mistaken for results of the new equation.

Open the linked run for progress and errors. After successful completion, recheck the intended time range. Archiving stops new calculations but retains existing history; restoration requires a rebuild and valid dependencies. See Runs and troubleshooting.