In installing flags (1" to 1 1/2" thick) on a 20' x 30' concrete patio
slab(which already has (away-from-the-house) pitch; what is best way to
maintain proper finished height of flags as they go down to keep that
pitch consistant?
A. String?
B. Set up side boards?
C. Use a scrap board ripped to the finished height depth as a guide?
D. None of the above.

Thanks