... you have to input the data for the gun and load, so to use them precisely you need to be a handloader with a chronographed load and have a rifle and scope combo that also has target turrets if you will to dial in the clicks ...
Alternatively
Buckdog, with the now generally reliable velocities communicated on the internet for the factory loads by the manufacturers, and with the ballistic coefficients (BC) communicated on the internet by the bullet makers, the $15 Shooter App on your iPhone/Android will produce a detailed 25 yd (or meters) increments ballistic curve in seconds, and you can just look from the 12 pre-loaded curves on the Leica "B" (for ballistic) models (either Geovid HD binoc/range finder combo, or CRF range finder), which one matches the most your curve.
If you want a higher level of technical precision, you can indeed purchase a $90 Caldwell chronograph and verify the load velocity out of your own rifle. Based on my experience, I would say that this is necessary if you develop your own loads to shoot steel at 1,000 yd, but NOT necessary if all you want to do is use hunting factory loads inside of 400 yd. So,
Rickmt, based on your self description I would not bother with a chrono.
In summary
1 -- check your factory load speed and its bullet BC on the internet;
2 -- get the $15 Shooter app for your iPhone/Android/tablet and get it to spit out the 25 yd increments curve for your load in table form;
3 -- compare your load ballistic table to the Leica pre-loaded 12 tables (printed at the end of the user booklet, and available on line);
4 -- select on the Leica device which curve you want to use (in my case with the 3 Wby loads I use most of the time, it is US 1 - the .257 and .300 loads are within + or - 1/2" from the Leica US 1 curve out to 400 yd, and the .340 is within + or - 1" from that same US 1 curve to 375 yd. My boys use the curve US 3 with their 7 mm Rem Mag 140 TTSX load);
5 -- select on the Leica device the output you want (in my case it is hold-over / hold-under in inches)
Note: you have the alternative options for clicks or equivalent horizontal distance;
6 -- sight your rifle for a 300 yd zero. Your ballistic table will tell you what it means at 100 yd for your load (in my case +2.2" @ 100 yd with the .257 Wby 100 TTSX; + 2.5" with the .300 Wby 165 TTSX; +3.2" with the .340 Wby 225 TTSX);
7 -- use and enjoy: all you then need to do is press the button. The Leica will measure the distance, the angle, the temperature and the pressure; it will correct for equivalent horizontal distance at the altitude you are; and it will display the flight path distance for 1 second, then the hold-under / hold-over: for example "- 2 " or "+ 4" which means you need to put the cross hair 2" low or 4" high, without worrying about angle, altitude, temperature, distance, etc. which are already all accounted for...
Really, it IS very SIMPLE, and it works. As previously stated it is hunting-life changing...
Thanx buckdog! I am not a highly technical hunter and my shots are under 350 always. I would not use the Leica features involving turrets etc .
Per the above, I am with you on this. I use the turret function when shooting steel at 600, 800, 1,000 yd and beyond, when I have all the time in the world; when I measure the wind; etc. etc. but not for hunting within 400 yd at the most, and 300 yd as a first shot self-imposed limit...
I hope this helps
Rickmt 
One parting thought: relatively, a $2,000 (sale price as they last) Leica HD- B 2200 is a great deal compared to a $3,000 Leica HD- B 3000, but a lower price option (also at Euro Optics) is the Leica CRF 2000 B. It is the range finder alone, but it does everything I just described ... for $400. Now, THAT is a steal...
