Is there a way to measure your traps with a tape measure?

I didn't know the right forum to put this in but how do you measure traps?

I'm seeing some progress in mine growing, but besides the mirror I'd like to try to measure it somehow if it's possible.

You could measure the length of them but that won't really change I know if mine have grown by looking in the mirror.

I know how i tell. I try on my old dress shirts and if they don't button at the top, they have grown.

you could use some sort of caliper to measure diameter. That'd be pretty accurate as long as you did it in the same place every time.