Now that you have your tape measure decoded, you may want to look at some marking tools. These are my recommended marking tools.
First up: Fine Point Sharpie
I use this for marking steel studs, face marking studs for electric box
locations, plumbing stubs, and anywhere I need a durable marker.
that you might want to paint. Do not use this on drywall unless you
want to spend a lot of money on KILZ to try to cover it up. This is a Permanent Marker
Next up: Carpenter Pencil.
This is the preferred tool for marking materials, as it has a strong lead, its shape is unique meaning you can find it in your tool pouch, and won't roll around. p.s. if you do a lot of business with specialty yards, they usually will give you a few. Even if you have to buy them, they are a good deal. Sharpen them with your utility knife.
Last up #2 Pencil
Everybody has them and they work. They do break easy, roll a lot and get lost.
Pens are not recommended as they run out of ink, roll farther and faster than #2 pencils.