WATCH REPAIR TUTORIALS & INFORMATION

You will encounter many watches with an unknown lift angle. The best thing to do is to learn to see the amplitude by looking at the balance arms. It's very easy with a 2 arm balance: from unwound, wind a tiny bit, just until the arms are coming right over the pallet fork, this is 90 degrees. Continue until the arms are switching places, this is 180 degrees. From there it's a matter of visualizing the further degrees; if it makes it to the arms directly over the pallet fork that's another 90 degrees, so you're at 270. Halfway there, another 45 degrees, so you're at 225. It's not too hard to divide a 90 degree quadrant into 4ths, you're in the realm of 20 degrees there (22.5).   I've found that the listed lift angle is off by several degrees or more just double checking the balance visually.    

FWIW, Fried recommended ‘graphite, molybdenum disulphide, or a mixture of this and heavy watch oil’

I've seen Rossi Giovanni RG Tweezers Italy for sale on ebay at a reasonable price, i can't find that much info or reviews online, are they a known brand that produce good quality tweezers, i need a no 5 to have a go at trying to repair my first hairspring, anyone have a pair of these are they ok.    

As @praezis an Laurie Pennman calculated correctly the rule of thumb should be 1/4 instead of 1/3

You are correct Old Hippy. You are limited as to what’s available  in the market place. And the closest you can get for the clock/watch you are working on as you say you may never fit the exact spring as it was made with.