About pressure set up.

[Flying Eye]

Hi all,

So, I've only been at this about a week or so by now, but something has been nagging away at me.

In EasyWeather I notice two pressure readings; one box is greyed out and looks like it may be a reference setting, and the other is open for editing.

Should this be edited at all and for any reason? And if so, then how does one go about getting that done right? I did search a while ago, but may not have been using the correct terms to find the right info about it.

Failing that what about calibration in general? Any tips on how one knows if it is calibrated right? Not sure if it's related or not, but my last "sensor lost contact" incident earlier this evening did see a large jump in pressure at about the same time, and I seem to vaguely recall the incident before that may have had that feature too. Not sure about the time before those two though. That is a lot of those for just over a week isn't it? It is possible stale batteries are afoot, so they will get replaced in the morning to hopefully avoid that for a little while!

I'd admit to being a bit puzzled about the pressure setting business.

[steve]

Your station measures the pressure due to the column of air at your location. This pressure is generally referred to as 'station pressure', or 'absolute pressure'. This reading varies with altitude, as the height of the column of air varies, so this value is not useful for meteorological purposes. It needs to be converted to 'sea-level' or 'relative' pressure so that everyone's readings are comparable.

You need to set the relative pressure on your station so that it is reading the same as a nearby reliable reading (e.g. from an airport or Met Office station), but ideally you would do this at a time when pressure is fairly stable, so right now in the UK is not very good time to do it - but it's better to do it and have it somewhere close if it's currently a long way out.

Someone has put some useful information in the wiki - http://wiki.sandaysoft.com/a/Pressure_Measurement

[Flying Eye]

Thanks very much indeed Steve, would 8 miles from where the runways cross be considered close enough to be useful? OR should I consider looking for other stations that are closer?

I always seem to search the wrong places, between the forum, 2 FAQs, a wiki and sometimes Google, it's hard to know where is the right spot, never mind the right question! I get the feeling I'd have more luck herding squirrels!

On top of all that I'd admit to not really getting along terribly well with the manual which came with it, I'm never quite sure who's side it's on.

[steve]

Thanks very much indeed Steve, would 8 miles from where the runways cross be considered close enough to be useful? OR should I consider looking for other stations that are closer?

8 miles is fine, that should give you a good reference point.

On top of all that I'd admit to not really getting along terribly well with the manual which came with it, I'm never quite sure who's side it's on.

The Fine Offset manual is quite poor.

[Flying Eye]

Thanks Steve,

I got it for now, of course I'll need to do this a time or two as the weather just isn't settled, but I got it to what feels like it's a lot nearer with a couple of tweaks so far.

Hope you won't mind me mentioning other free software, but I got this, and find it very handy for just aviation reports http://www.nirsoft.net/utils/mweather.html

It's very useful for this sort of thing as you can set up just aviation report centers near you!

In slightly "other" news, with all this tweaking I'm doing resets and clearing out data fairly often, it's irritating for sure, but in my heart I know that I'm working towards "the big reset" just after midnight on the new year, and then we'll see about it all!

Amazing what you can do with a screwdriver a pair of cutters and some cable clips, I made nearly half a metre of rain in just 40 minutes this morning! However the rain gauge is lower than before and today my temp sensor is now at 1.5 mtrs +/- 5cms (not sure how far up the plastic sensor box it lives!)

I am going to attempt to make a Stevenson screen soon I think, and I am thinking of using a tool stand to mount it on, ok, it's blue not white, but I'm sure that'll be fine, for only 20 quid it's got to be a winner I suspect. Hope this lot all starts behaving (electrically speaking) soon. It's had new batteries this morning too, so fingers are firmly crossed!

I've got it down to 3.8 metres and clear line of sight horizontally through 1 double glazed window. If it can't stay on track with all that help going for it, then it's not the unit for me I suspect. Could be a duff one I suppose.

[Flying Eye]

Steve,

Would 16.5 miles be too far to be useful?

It's just that my local at 8 miles is only during office hours or something no so helpful like that. Also does not post until the data is a good 9 minutes stale.

The one at 16.5 miles away is 24/7 manages to post twice an hour and is more or less on time, well it posts only 3 minutes after actual time stamp.

What sort of distance should I consider to be too far to be useful in general?

[steve]

If the pressure was quite stable (a large slow-moving high pressure system), that would do fine. But right now in the UK is not a good time to be setting barometers at all.

[Flying Eye]

Thanks very much Steve.

With all the resets dictating the pace, I'm not bothering to set it at all now, have moved over to adjusting in Cumulus.

Just working out which airports I should consider using, hence wondering about maximum distance I should include or reject as a rule of thumb.