[Avodah] reading thermometers on shabbos

[Zev Sero]

Gershon Seif wrote:
> My understanding is one may not set up a thermometer on shabbos as it
> falls under the issur of medida.
> 
> But may one read a thermometer that was put in its place before
> shabbos? ie. a large weather thermometer hanging in the backyard 

Why not?  How is it different than reading a clock that has already
been set up to run before Shabbos, or a ruler that is already in
position from before Shabbos?

-- 
Zev Sero                      The trouble with socialism is that you
zev at sero.name                 eventually run out of other people’s money
                                                     - Margaret Thatcher