Thanks again Linuxboy! I expect some differneces to occur when I try calf rennet. Will be interesting to see how close I get with these calculations.
And, in case anyone else is interested, basically, if you switch rennet, and now have something with a different strength, to get an estimate of how much of your new rennet to use, do the following:
New Amount = Amount of rennet normally used X (IMCU original rennet)/(Litres of your previous makes) X (Litres of your new make)/(IMCU of your new rennet).
So, for example, if I was using 0.6 ml of 750 IMCU strength rennet for a 10 L make, and then buy this 180 IMCU strength rennet, how much should I use in my next 10 L make?
New amount = 0.6 X (750/10) X (10/180)
New amount = 2.5 mls.
And, interestingly enough, the range on the bottle was 0.2 - 0.5 ml per litre, so 2.5 for 10 Litres sounds about right. It's also at the low end of their suggested dosage, and my use of 0.6 is less than the 0.7 marked on my current bottle (current rennet has no "range"; and 0.7 converts to 2.9 ml).
Anyway, once I actually pick up some new rennent to try this, I'll report on the results.
P.S. I've put an excel work sheet that will do this calculation for you. Also, this booklet has a page that I find very useful when having to slowly increase temperature over 30 or 40 minutes. Just enter your temperature readings every so often to see if you're "on target" or too warm or too cool.