How to measure around a circle's circumference?

I’m using Sketchup 2017. I’m trying to create a 3D model of a real world object. It’s a cylinder that has “windows” cut out around its circumference. I’m having trouble getting these windows spaced properly. I can measure the spacing by wrapping a flexible tape measure around the object but when it comes time to draw in SU I’m forced to eyeball the distance from above. Is there any way to select a point and measure around the circumference instead?

The simplest way is probably to draw the cylinder using a number of sides that is a multiple of the number of windows. Then draw one window and array-copy it around the cylinder using the rotate tool about the center axis of the cylinder. Rotate one copy to the next position by counting how many cylinder sides you move through. Then type (e.g.) 5x to repeat the copy that many times around.

The final model will need to be finely detailed. The windows are fairly large, but of different sizes, which would turn the cylinder into a brick if I made any side the width of any given window.

Attached link shows what I’m drawing. Windows on any given section of the cylinder can vary in width and height http://donkriminfo.dn.ua/attachments/sport-ohota-rybalka-166/32692d1359407259-prodam-vphr-voiskovoi-pribor-himicheskoi-razvedki-s-hraneniya-79967387_2_644x461_prodam-vphr-voyskovoy-pribor-himicheskoy-razvedki-s-hraneniya-fotografii.jpg

As i’m sure you know all circles are made of segmented edges. A circle will show the circumference in Entity info, which is actually all those segments added together. If you explode the Curve you can select some of the edges and their length will be added together and shown in Entity info.
So you need to decide how many segments you want to get as close to the size as possible and how smooth you want it.
Circ
The fact that I got the same measurement in the gif twice was coincidental.

Guess that"s about as close to what I need as I’ll get. I appreciate it!