I Units of Flatness
The formula for I - Unit calculation when manual measurement is involved is

I = 2.47 (f / L)2 x 105

where f is the wave height and L is the cycle length. This formula is derived from the assumption that the deviation from flatness follows a sinusoidal wave form, as illustrated below.

According to this formula, an out-of-flat condition of 0.125" height in a 18" cycle calculates to 12 I Units.


Height
(in.) 		Wavelength (in.)
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
1/32
0.0312 		4 3 2 2 2 1 1 1 1 1 1 1 1 0 0 0 0
1/16
0.0625 		15 12 10 8 7 6 5 4 4 3 3 3 2 2 2 2 2
1/8
0.1250		 60 48 39 32 27 23 20 17 15 13 12 11 10 9 8 7 7
3/16
0.1875 		136 107 87 72 60 51 44 39 34 30 27 24 22 20 18 16 15
1/4
0.2500 		241 190 154 127 107 91 79 69 60 53 48 43 39 35 32 29 27
Download
this page in
PDF format
PDF | 71 KB