Gotta be quick... only have about 10 minutes.
The conversion factor is the d2 constant, which is an old shortcut method for quickly estimating standard deviation. It is widely used to set three standard deviation limits in Control Charts, and has been for about 100 years.
For small groups of data, say 5 items, it is very nearly as efficient as standard deviation, and does not have the problem of systematically underestimating variation. By the time you get to groups of 10, its efficiency is beginning to fall off quite a bit.
There are several ways to estimate standard deviation, and typically none of them will give exactly the same answer. However, most of them will provide decent accuracy.
To convert range to SD, you divide range by the d2 constant:
For groups of 2, d2=1.128. For 3, 1.693. For 4,2.059. For 5, 2.326. I'll post the rest after my meeting.
