they also make belt tension deflection measuring tools for those applications

Maybe this might not make any sence but here goes. Has anybody Plucked the belts and listened for the sound it makes?.Equal tension should make the same sound. LIke tuning a guitar.I have a TIN ear so I can't realy tell.

That has been discussed at length and is how I adjust/tune my belts and also fish line.  I would disagree with the statement "If your belts resonate they are too tight".  I would take that one further and say if they don't resonate they are too loose.
All that being said, I think we all have valid ideas and things that work for us and our printers
Find what works for you and stick with it.

Maybe this might not make any sence but here goes. Has anybody Plucked the belts and listened for the sound it makes?.Equal tension should make the same sound. LIke tuning a guitar.I have a TIN ear so I can't realy tell.

if belts resonate then they are too tight ;^P

I have replaced the x/y rods and carraiges,belt tensions appear to about equal.   I just can't get a Perfect circle, best I got so far is .13mm  out of round.Am I too picky?  LOL

yea wher is the deviation you should measure in 4 places not 2.
also would not hurt to run a cube.  if the sides of the cube are not equal you will want to adjust steps.

+- 0.005 inches is a pretty standard general machining tolerance.
if you want to build a working steam engine with your print you may want a more precise round circle.
General carpentry plus minus 1/8 .125 in
Finish carpentry +- .0625
Cabinet makers +- .032
Machining layout +-.015 in
A lot depends on what you are doing with your parts you make and how precise you need it.
There is an old saying in machining precision is expensive and not always a good value.
Young engineers often specify a higher tolerance than what is needed . and this increases the cost of machining.
Additive manufacturing is a bit different. once the part is made you can not add a lot .

comes back to how precise does it need to be how much time do you want to spend tinkering and would you rather just use the printer.
Tin

http://www.soliforum.com/topic/8357/y-s … belt-slop/