I'm building up my Raleigh Professional Mk IV and am at the stage of fine tuning things. I frequently mark positions with a bit of masking tape (seat post height, stem height, handle bar angle) with a small bit of masking tape. Ex: sorting out the angle of the handlebars - higher or lower or just right. I need to make really small changes then test ride. I put a small strip of masking tape on the joint where the bar meets the stem clamp. I then carefully cut along the joint with a sharp blade and now one half is on the stem and one half on the bar. Then as I rotate the bar up or down the masking tape shows me where I was and where I am now - sometimes just 1 degree changes. I'll probably not settle this out until after a few 30 mile rides.
I'll use these on the seat post and stem - mark a position then raise it 1/8 inch then see how that feels. Go too far then back off. Or mark the seat angle and make adjustments, or the seat position fore and aft. When I've decided AOK, I pull all the tape off and just ride.
I've found blue painters tape falls off to easy. Just regular tan masking tape.