411A, you are right about the tilt calibration -- rarely will the "indication" equal the actual tilt.
Easiest way to "calibrate" it yourself for each flight is to use the 100'/1nm rule of thumb. Tilt down till ground return = height (not altitude AMSL) in thousands. Eg F350, closest ground return @ 35 miles. Bottom of beam is 10 degrees down. You do the maths.
Generally speaking, according to company 'coneheads' a 10 inch diameter wx radar dishes produce a beam 8 degrees wide, and the beam width reduces by one degree for each increase of one inch diameter of the dish. Generally speaking. Writer makes no warrantee as to the accuracy of above statement. Break the habit of a lifetime and talk to a radio tech yourself before you sledge me. Even better -- ask the radtech to find out the beamwidth for your installation from the bucketload of manuals he/she has.
Armed with those two slightly dodgy bits of info, you can then do some more 1/100 with your tilt in flight and come up with handy guesstimates. Not accurate to the millimeter, but we don't give our ETA to the decimal of a second either.
[ 05 November 2001: Message edited by: ITCZ ]