Resurrecting this old thread to keep my question in context. I'm writing software to convert the output stream from Gary's Wunder Weather Station to Cumulus, using its EasyWeather.dat file import mechanism. Steve posted
http://sandaysoft.com/forum/viewtopic.php?f=10&t=5683, in which he says: "You should be reading and reporting relative pressure. This is the pressure corrected for your altitude, and it means that everyone reports values which correlate, regardless of their altitude." The import mechanism asks for both absolute and relative pressures, so the goal was to compute absolute pressure from the elevation-corrected pressure gather from the WWS.
I came upon this WXForum thread and tested the equation from @SoMDWx in Excel. I am a bit confused now, either by the definition of relative pressure from Steve, or by the discussion here. From the OP's question, the equation should give relative pressure from absolute, but it appears to provide absolute pressure from relative. Using a pressure of 29.92", here are some examples: at zero elevation, the equation result is 29.92". At 5,000' elevation, the equation results in 24.89", while 10,000' results in 20.57". Thus, I concluded the equation provides absolute pressure from relative pressure.
If anyone can help me understand my mistake, or clarify the definitions here and in Steve's Cumulus post, I would sure appreciate it.
Thanks... Randy