In my sons room, I picked a nice one up at a boot fair for 50p & gave it to him when he was 14, His grandad showed him how to use it. A few weeks later a maths teacher at school saw him using it & had to be enlightened as to how it worked! He still uses it occasionally.
I still have my french curves & a pile of splines of various sizes also a planimeter used for measuring areas.
I also like designing on the fly by eye. Proverbial back of a fag packet stuff.
Is there a science to french curves? Ie are they a standard curve or based on some maths somewhere? I have a set which I had since school but don’t use them much. I always wondered how they arrived at the designs of them.