HalHoff:
X=(61.57181-62)/(61.57067-61.57181)+1
X=376.6
Well done with this I'm sure almost everyone here will understand that but as the precision of maths is beyond my ken (looks to me something like -.43 / -.00114 +1 =376.6 :-/, I know it's my bad) I need to bludgeon it with arithmetic.
An average of 61.57067 changes to 61.57181 after a 62 and played a lot at the tier.
400 rounds would = 27,628.2684 strokes + 62 / 401 = would change it to 61.57174. So the average hasn't changed enough meaning you've played fewer than 400 rr's.
350 rounds = 21,549.7345 + 62/351 = 61.57189. Now it's changed by too much.
400 rounds was .0007 too little a change and 350 rounds .0008 too much, I'd probably have got close next time :-)