I really recommend circular slide rules! Search "Concise circular ruler" on Amazon for a great quality but affordable slide rule. There's a couple of differen

I really recommend circular slide rules! Search "Concise circular ruler" on Amazon for a great quality but affordable slide rule. There's a couple of different ones so pick the one that has the functions you'll want. Also, there's a bunch of watches with slide rules in the bezel. I have a citizen promaster on my wrist that is super handy for stuff like this.