Another interesting low cost option, that doesn't require batteries, is Accuracy 1st's whiz wheel. You send them your ballistic data for 3 different loads, or loads for 3 different cartridges, and they will make you up a whiz wheel that takes into account: barometric pressure, wind, spin drift, moving target holds, inclination correction, and velocity corrections for +/- 50 fps which provides a correction for chronograph readings or BC. Firing solutions are provided for short, medium, and long range. The card I have on mine right now is for a Matrix .308/210 gr VLD with a G7 BC of 0.326 and a velocity of 2650 fps. You get to choose the values the wheel is calibrated for, so I chose to have the firing solution based on yards and the correction in mils, the maximum range that this wheel can calculate for is 1560 yards. The day this thing arrived, my wife and I went out to the range, it was a warm calm evening, lazed the 12" steel at 850 yards, plugged the data into the whiz wheel, got a firing solution of 7 mils, put 7 mils on the scope, sighted, pressed the trigger and a few seconds later was rewarded with a solid clang! "Well, that was boring, I guess we can go home."