:
Ha, Vince you beat me too it!  Except my measurements are a little different?:
290
220
270
280
160
110
180
310
140
310
------
310
320
210
330
310
320 |
You're right. I made a few mistakes - was in a bit of a rush
The best thing to note though is that we both found them to be EXACTLY (almost up to the decimal) on quantities of 10.
I will update my initial post as well.