Chrono distance

You are on the range and your measure you bullet velocity to be 3000fps at 9 feet/3 yards, using a chronograph. Your need to know the muzzle velocity, to print a ballistics table.
What is the velocity at the muzzle? Your ballistics software will tell you, 3012.9 in this case:

This is where mobile software is so great. You can measure velocity, type it into your phone and you have all the adjustment information at you fingertips instantly. You don't have to go home to your desktop computer.

But if your software doesn't have that feature, how would you work it out?

Put in 3000fps as your muzzle velocity, you lose 14.9fps (3000 - 2985.1) in the first 3 yards.

So estimate the muzzle velocity to be 3000 + 15 = 3015:

 

3002 at 3 yards is over by 2, so subtract 2 from the 3015:

 

So now we are 3000.1fps at 9 yards, which is close enough.

Thank heavens for computers!

From my mailbox:
For example, my math for 500 yds is:  bullet drop (in inches) divided by 1.25 inches (where 1.25 is the click value at 500 yds using a ¼ MOA).  So if the drop is 64 inches at 500 yds (according to your ballistics table for the REM Core Lokt 223), then 64/1.25=51 clicks; however, your software says it is 49 clicks.

The math is:

(((4 * 100) / 500) * 64) / 1.0472 = 48.8922842

If you put 50 shooters in a room with the above question, you could come back the next day and nobody would agree. And probably nobody would be right. So put the pencil and envelope away and use a ballistics program. 
(1 Moa is 1.0472" at 100 yards).

How do I use a ballistic calculator to shoot things?:

You have to get the Big 6: BC, Muzzle Velocity, Sight Height, Zero, Pressure and Temperature.

BC is probably on the Ammo box, or look it up on the manufacturer's website.

Muzzle velocity you measure with a chronometer. Or look it on the Ammo box, or look it up on the manufacturer's website, that will be for a generic barrel length.

Sight height, distance from muzzle center to front sight tip or Scope front center.

Zero, whatever distance you zeroed at.

Pressure and temperature from a weather website for your area. This will vary.

So type in the above values, type in the range to the target, and you will see the drop in inches and the number of clicks (1/4 Moa) to adjust the vertical elevation turret for the drop. Most people aim off for windage, or you can use the number of clicks on the windage section.

If the drop is 6" and 15 clicks, you aim 6" high, or turn the elevation turret in the direction of the scope's "up" arrow 15 clicks. It is good to mark the elevation and windage turret positions when you zero the rifle. If the calculator says go up 30 clicks for a different range, that is 30 clicks from your zero setting.