Pressure readings

[RCweather]

Hi

Got my new WH2080 from Santa - very happy so far after getting Cumulus instead of Easyweather! Slight problem though, the readings i am getting off my receiver are different to those on the Cumulus program. For example at the moment the handheld device is reading 1010.1 hpa (abs) which for a start is different to the barometer reading i have which currently saying 1015 but my cumulus is reading 1038.1 hpa. i read on the FAQ page

"If your relative pressure still disagrees with the Cumulus display, it may be due to the following: The Fine Offset stations only supply absolute/station pressure to Cumulus, so it has to adjust to sea level. When Cumulus starts, it reads the pressure ‘offset’ (the difference between absolute/station and relative/sea level pressure) from the station so it can use it subsequently to calculate the sea level pressure. Sometimes the offset that is read is clearly garbage, so Cumulus uses zero as a best effort.

To circumvent this, you can edit cumulus.ini, and in the [Station] section add an entry:

EWpressureoffset=x.y

where x.y is your pressure offset. Cumulus will then use this instead of reading it from the station.

Note that you must supply the offset in hPa (the units that the station works with). "

However i can't understand this or work out how to edit 'cumulus.ini'

If someone could help i'd be ever so greatful

Thanks in advance

RCweather

[steve]

The cumulus.ini file is in the Cumulus program folder - i.e. the same place as cumulus.exe. But before resorting to that, you need to look into the part of the FAQ that you haven't quoted. You need to set the relative (i.e. sea-level adjusted) pressure on your console so that it's correct, and then Cumulus will display the correct value. Instructions for setting the relative pressure should be in the manual for your weather station.

[peterh]

If your barometer is a mechanical unit, I would expect that it would give you an absolute value, because it does not know what your pressure relative to sea level is. In that case, your barometer and the WH2080 console (set to give you the ABS value) should give you the same value. If they don't, one of them is wrong. I have an older mechanical barometer of unknown reputation, which gives a reading that is about 4 hPa off... and I *know* that in my case, the barometer is wrong.

For each 8 metres over sea level, the absolute pressure decreases with 1 hPa. On some weather stations, you can just enter your elevation above sea level, but for these units (at least for the WH3081 that I have), you should do the math yourself. So, if, say, you live 100 m above sea level, you should configure the WH2080 to add (100 / 8 = ) 12.5 hPa to get the pressure relative to sea level.

That is what I did with my WH3081, and lo and behold, the values that I get from Cumulus correspond fairly well (to a few tenths of a millibar) to what the official KNMI weather station closest to my location comes up with. The KNMI is our equivalent of the Royal Met Office, and their weather station closest to my location just so happens to be their head office. I have seen the stuff that they use to acquire and interpret data, and it is the stuff of legend, way beyond what we can even begin to imagine. If I would have 0,1 percent of their computing power, I would be entering this post not through a keyboard, but through a direct brain link, and I would've answered this question before you typed it.

Anyway. If you have set up your WH2080 (more specifically, the correction for absolute to relative pressure) correctly, you should normally not get bogus data in Cumulus, and you should therefore not have to edit your cumulus.ini file.

If you cannot get it to work properly, don't hesitate to get back in touch... but I would suggest that you would compare whatever you get with a measuring station local to you. Having said that, I've been looking at the weather maps over the last couple days... I think it's fair to state that no place in the UK hasn't had 1035 hPa on Dec. 27. In order to get that value over the last couple days, your station would be configured to be (wild ass guess) at least 80 metres higher than it is.

[RCweather]

If your barometer is a mechanical unit, I would expect that it would give you an absolute value, because it does not know what your pressure relative to sea level is. In that case, your barometer and the WH2080 console (set to give you the ABS value) should give you the same value. If they don't, one of them is wrong. I have an older mechanical barometer of unknown reputation, which gives a reading that is about 4 hPa off... and I *know* that in my case, the barometer is wrong.

For each 8 metres over sea level, the absolute pressure decreases with 1 hPa. On some weather stations, you can just enter your elevation above sea level, but for these units (at least for the WH3081 that I have), you should do the math yourself. So, if, say, you live 100 m above sea level, you should configure the WH2080 to add (100 / 8 = ) 12.5 hPa to get the pressure relative to sea level.

That is what I did with my WH3081, and lo and behold, the values that I get from Cumulus correspond fairly well (to a few tenths of a millibar) to what the official KNMI weather station closest to my location comes up with. The KNMI is our equivalent of the Royal Met Office, and their weather station closest to my location just so happens to be their head office. I have seen the stuff that they use to acquire and interpret data, and it is the stuff of legend, way beyond what we can even begin to imagine. If I would have 0,1 percent of their computing power, I would be entering this post not through a keyboard, but through a direct brain link, and I would've answered this question before you typed it.

Anyway. If you have set up your WH2080 (more specifically, the correction for absolute to relative pressure) correctly, you should normally not get bogus data in Cumulus, and you should therefore not have to edit your cumulus.ini file.

If you cannot get it to work properly, don't hesitate to get back in touch... but I would suggest that you would compare whatever you get with a measuring station local to you. Having said that, I've been looking at the weather maps over the last couple days... I think it's fair to state that no place in the UK hasn't had 1035 hPa on Dec. 27. In order to get that value over the last couple days, your station would be configured to be (wild ass guess) at least 80 metres higher than it is.

Thanks for the reply, I had to manually manipulate the relative pressure to my altitude (78m, well guessed) and now cumulus is readif correctly as I can compare it with a barometer we also have that is accurate to stations around me. Thanks for the help!