StdCalibrate Altimeter

[rich T]

I'm trying to adjust my Altimeter reading ( -0.07 inHg off) to be aligned with the local METAR Altimeter reading. In the weewx.conf, I added the following:

##############################################################################

#   This section can adjust data using calibration expressions.

[StdCalibrate]

    

    [[Corrections]]

        # For each type, an arbitrary calibration expression can be given.

        # It should be in the units defined in the StdConvert section.

        # Example:

        # foo = foo + 0.2

        altimeter = altimeter + 0.07

I restarted weewx; waited an archived period and the altimeter value did not reflect a 0.07 change. Do I need to change something else? I'm currently using Weewx version 4.0.0b12.

Thanks

Rich

[gjr80]

When it comes to any of the ‘pressures’ you need to be very careful because the behaviour depends which of the three your station provides. If your station does indeed provide altimeter then StdCalibrate should work as you have specified (field altimeter will exist when StdCalibrate is applied). When StdWXCalculate comes along afterwards it will not calculate field altimeter as it already exists. However, if your station does not provide altimeter, you can’t calibrate it (field altimeter does not exist) but StdWXCalculate will come along afterwards and calculate altimeter, so it can appear that altimeter was not calibrated. It’s worthwhile having a look at the order of the process_services under [Engine] in weewx.conf.

So have a look at your station/driver, what ‘pressures’ does it emit? If it does not emit altimeter then you can’t use StdCalibrate, all you can really do is calibrate the ‘pressure’ that is emitted (and altimeter should follow from that).

Not sure but I could see software record generation also causing some unexpected results, not 100% sure on this, would need to have a look at the code base and am unable to do that just now.

Gary

[mwall]

On Sunday, May 10, 2020 at 10:27:34 PM UTC-4, rich T wrote:

I restarted weewx; waited an archived period and the altimeter value did not reflect a 0.07 change. Do I need to change something else?

rich,

unless your hardware reports it, altimeter is a derived variable - it is calculated from pressure.

the corrections apply only to independent variables.

m

[rich T]

Thanks Gary and Matt. The station I'm pulling data from emits station pressure. I just assumed that if you applied a calibration correction for any one of the pressure types the other two pressure types would follow.

Rich