i just bought an sa arf today, it says when making the control linkages that you will need to make them lengths like 34.8 millimeters and trying to get them perfect to a tenth of a mm is pretty hard. do these have to be exact?

As close as possible. Once you spool it up you'll probably have to do some minor adjustments anyways to get it just right.

With a digital caliper you can't go wrong,the manual is just a reference guide
After your initial flights, you have to re-adjust them again. An of course it all
depends on motor,batt & esc. Good luck...

The linkages being perfect are very important to the success of your heli and advancement. If the heli is not close to perfect you will be fighting that heli instead of learning to fly. The specifications/measurements are there for a reason. Get a digital caliper and be happy you did.

Example: If you wear a size 9.5 shoe and you purchase a sized 9.0 more than likely you will be able to get your foot in it, but it will cause you to walk different instead of walking normal. You will have to work harder to counter the pain.

The same with a heli when setup of right.