Just buy a set of scales. you will be much happier in the end.
You can always show up early and pay to borrow somones at the track.
You wont have to ask long before somone throws out a price.
The most basic scales work close to the most advanced. If you know
how to do the math you dont have to have all the functions.
If your swapping springs and changing alot for different tracks it would
cost alot to bring it to somone else constantly.