Table 2: Rebound curve for concrete strength measurement and error.

Regress model Function expression Correlative coefficient Mean relative error (%) Relative standard error (%) Exponential function 0.824 12.43 15.33 Exponential function 0.850 11.88 14.7 Logarithm function 0.868 11.21 16.88 Power function 0.850 11.17 14.05 Power exponential function 0.824 12.43 15.33 Complex-exponential function 0.852 11.04 13.75