Input
Results
Mean R—
Std dev s—
CV %—
Orientation correction—
Corrected R—
Estimated f'c—
5th-percentile (μ − 1.645·s)—
Method
Average 10 readings, drop ones varying > 6 from average. Orientation corrections (typical): horizontal 0; down +2.4 to +3.5; up −2 to −3 (varies by R-value). Strength fits: standard f'c [MPa] ≈ 1.05·R^1.155 (rough). Manufacturer curves preferred. ACI 214.4 recommends using 5%-percentile as design value.