Re: tunning my tartan 30
My guess is that you would be very lucky to find a Loos Gauge on the boat. Probably about 1 in 25, or less, have them.
There has to be a website community for your boat. Go there and ask the question about tension, rake, etc. Or just do what many do and get the mast in column, tighten the shrouds and backstay, assume that the PO already had the headstay correct, and go sailing. In 10 knots you should be slightly loose on the lee side. If real loose tighten both side a little and try again.
If you get it perfectly tuned you are one of the few, including myself who is anal about it, to get it perfect.