# [StdCalibrate]

The `StdCalibrate` service offers an opportunity to correct for any
calibration errors in your instruments. It is very general and flexible.

Because this service is normally run after `StdConvert`, the units to be used
should be the same as the target unit system chosen in
[`StdConvert`](../stdconvert). It is also important that this service be run
before the archiving service `StdArchive`, so that it is the corrected data
that are stored.

In a default configuration, calibrations are applied to observations from the
hardware. They are not applied to derived calculations since the
`StdWXCalculate` service runs after `StdCalibrate`.

## [[Corrections]]

In this section you list all correction expressions. For example, say that you
know your outside thermometer reads high by 0.2°F. You could add the
expression:

    outTemp = outTemp - 0.2

Perhaps you need a linear correction around a reference temperature of 68°F:

    outTemp = outTemp + (outTemp-68) * 0.02

It is even possible to do corrections involving more than one variable.
Suppose you have a temperature sensitive barometer:

    barometer = barometer + (outTemp-32) * 0.0091

All correction expressions are run in the order given.

Both LOOP data and archive data will be corrected.

If you are using a Davis Vantage instrument and all you require is a simple
correction offset, this can also be done in the hardware. See your manual
for instructions.