I was taught (hort college) to use a flat object to measure average mowing heights-- a notebook, a 12 inch 2x4 piece of wood, etc.......then get down on my hands & knees with a ruler at a horizontal angle to measure exactly what the average mowing height of recent grass blades ended up to be after the lawn was mowed/trimmed. Keep in mind that this does NOT include "high spots" in the lawn where lawns are scalped. Kentucky bluegrass should be mowed at 3 - 3 1/2 inches during summer according to my land-grant university (ISU). Prob is .... most homeowners mow at 2 1/2 or less. Sometimes at 1 1/2 inches at best. Then they blame us because they have drought damage, spurge & crabgrass, sod webworms, etc. We measure their mowing/trimming height---------if it's short, we leave them a land-grant university fact sheet regarding low mowing/summer burnout/crabgrass. Anybody else have ****** customers who butcher their lawn - then blame you? p.s. I mow my own lawn (2 acres) at 3 inches or higher. Never treat for crabgrass, and I never have any crabgrass or dead areas.