Do you have a measuring tape? Do you know how to read it? I've used measuring tapes all my life. Today I finally realized why all the 16" marks are red. (16, 32, 48, etc) Wall studs are 16" apart. It's a heck of a lot easier to stretch out your 30' line across the whole wall and just quickly walk down and mark all those red lines!
Now, class, raise your hand if you never knew why 16" were marked red... :D