"Zak" wrote:

After carefully comparing rainfall using both the Davis VP and a standard
manual gauge it seems, in calm weather, my VP is under-reading by 20%. The
tipping mechanism is clean and moving freely.

I know the two screws under the tipping buckets need to be turned
anti-clockwise in order to lessen the amount of rain required to tip, but
can anyone suggest the amount they need to be turned in order to achieve
the 20%?

Sorry to come to this thread so late ... and following all
the other excellent advice all I am going to do is repeat
the Eden mantra which applies to anyone and everyone
with an AWS ... however fantastic your AWS is,
please add a traditional manual rain-gauge to your site;
it is the only way you will achieve a rainfall record
under standard conditions, comparable with all official and
historical data (with the proviso that your site characteristics
should also be as close to the official standard as you can
manage).

Philip