eliqunn has experience with the '88 924S & 944s.
I reread the explanation a couple of times to understand his method.
Reposting an explanation from Van on Rennlist who has done a few DIY videos helped me.
I do not recommend buying any version of the Krikit belt tension tool. It is sold locally at NAPA, KR1 I think, it also is sold as the Optibelt tool, and a few other names.
You will not get an accurate reading with the tool on the cam belt.
I use it for the balance belt to get close---(the belt will feel real loose with any method).
If you have fears or nightmares about bending valves when the belt slips or about the correct tension, get the Arnworx tool. Many reviews on the accuracy of the expensive set. I have not used the new $50 tool to advise but Bruce Arnn is methodical -- compulsive in the tension process.
GL
John