There's an excellent book on weather radar called Airborne Weather Radar, A User's Guide by James C. Barr. Book is everything you would ever want to know about weather radar. I've read it probably 10 times and keep cheat sheets in the plane.
It all starts here (figure out what size dish you have, most light GA stuff has either a 10 or 12 inch antenna):
30 inch antenna = 3-degree beam
18 inch antenna = 5-degree beam
15 inch antenna = 7 degree beam
12 inch antenna = 8 degree beam
10 inch antenna = 10 degree beam
Why is this important? Well, we need to figure out what our beam width is at a given distance. Here's a formula for determining this:
Distance (NM) x 100 = beam width in feet per degree of beam angle.
For example, 40 NM x 100 = a beam width 4,000 feet wide per degree.
If you have a 10 degree beam, then the beam width is (10 degrees x 4000 feet) = 40,000 feet at 40 NM.
Now you need to figure out what is actually "filling" the beam. For instance, if you are at 40 NM and you have a 30,000 ft thunderstorm in front of you, it doesn't fill the entire beam width and can be devastatingly understated on the screen.
Now is where tilt management comes in. We must be able to paint the storm from the ground on up. For example, if your pointing your antenna at the upper 1/10th of the storm, you are overscanning or if you have your tilt set too low, you are underscanning, which is really bad. Therefore, we must be able to establish a ground base (or zero tilt). Here's the formula to determine zero tilt:
Take 2 zeros off your altitude, and divide that number by half of your beam angle.
Using our previous example, we are at 10,000 ft and we have a 10 degree beam. The true zero tilt position should begin to paint ground returns at approximately 20 NM.
(10000/100) / (.5 x 10) = 20
Sometimes the zero tilt mark on your radar is not correct, so use that formula to calibrate the zero tilt.
Now, we already know that if we are using the 40 NM scale on the radar screen, each degree of tilt is equal to 4000 feet. So if we establish our zero tilt and we see ground returns at 20 NM, we can scan what's in front of us by tilting up one degree (4000 ft) and we can basically tell how tall a thunderstorm is or where the precip begins and ends relative to altitude. This all assumes that what you are painting is reflective (rain and wet snow).
There's a ton of other stuff to learn about weather radar (attenuation, gradients, ground tilt management, shapes, etc), so I would highly advise getting the aforementioned book.
I just put a new RDR2000 in my baron and have made 4 trips back and forth to FL recently. On every trip, I've had to apply these principles and they have worked like a charm everytime.
