I used to eyeball every course level and then a foreman in Des Moines handed me a 4 foot Stabila
For 8 seasons I laid to a chalk line and just trusted my eye on each course, and honestly I got away with it on most walls. Then last spring a foreman named Duane on a job in Des Moines made me check my work with his 4 foot level on a 12 foot run and I was off a quarter inch by the top. Now I keep a level on the wall every third course instead of just at the ends, and my corners come out dead on. What are you all using to check level on long runs, or do you just trust the line?