You can adjust the shrouds with the folding rule method but a more easy way is to use a rig tension meter.
The only problem is to buy one since most of the tension meters cost a lot of money. Today I have bought a cheap swedish made tension meter and I show how to use it.

note : If the turnbuckle squeaks stop tightening this is a sign of overtightening and poor lubrication.

You can get the tension meter in 4 different sizes :

2.5 4 mm. wire 77 US Dollars
4 6 mm. wire 86 US Dollars
6 8 mm. wire 90 US Dollars
8 10 mm. wire 103 US Dollars

Bluewave smartpin :

VP1020 : 1/4"
VP1225 : 5/16" 3/8"
VP1632 : 7/16" 1/2"
VP2340 : 5/8" 3/4"

price around 26 US Dollars, possible to buy at svb.de