You've got to take several things into consideration. How much does your actual draw length vary, plus or minus, from 30"? Longer is faster, shorter is slower. How much does your arrow weight vary from 350 grains? Lighter is faster, heavier is slower. How much does your draw weight vary from 70 pounds? What string accessories - silencers, peep, kisser button, nock sets, string loop - do you have mounted on your string? Each thing you put on the string slows your arrow speed.Do you shoot release or fingers? Fingers release generally gives slower arrow speed.

I used to know how much to add or subtract for all that stuff to get an approximate speed, but I must be coming down with old timer's disease.Can't remember any of it now.[&:]

Even after all that, then you have to wonder if they were completely truthfull when they listed the IBO speed. Some manufacturers aren't.

The only real way to know how fast your bow is shooting is to put an arrow across a chronograph.