Home > News > Scratch And Dig numbers-By ISO standard 10110-7
Scratch And Dig numbers-By ISO standard 10110-7

Lens Cleaning Figure 1

In 1996, the ISO issued standard 10110, which was basically taken from the German standard DIN 3140. It has since been adopted as a national standard by Germany, Japan, France, Russia and other nations, and is used in many others, including increasing numbers in the U.S., notably for the National Ignition Facility. At the time of writing, the most recent version was ISO 10110-7:2008.1

One of the ways the ISO standard differs from those discussed above is the way it categorizes surface defects. The very concepts of scratches and digs are closely related to the historical process of grinding lenses with abrasives. The ISO standard instead approaches the problem strictly from the perspective of dimension. Instead of digs, the category “localized surface imperfections” includes not only digs but also any scratch shorter than 2 millimeters. Longer scratches then fall into the category “long scratches.” The square root of the total defect area for a region is the grade number for that region.

Under this standard, a specification of surface quality takes the form:2
5/X × Y;LZ × F
for example, 5/1 × 0.05;L5 × 0.004
The “5” is a header indicating that this is a designation of surface quality. The “L” is another header; it identifies the part of the designation that deals with “long scratches.” The other elements are as follows:
X is the maximum number of digs the part can have at the dig size specified by Y.
Y is the maximum dig size, in millimeters.3
Z is the number of scratches
F is the width of the widest scratch, in millimeters The available grade numbers are 0.004, 0.006, 0.010, 0.016, 0.025, 0.040, 0.060, 0.100, 0.160, 0.250, 0.400.

At the time of writing (summer 2010), the U.S. is in the process of adopting as an American National Standard (ANSI/OEOSC OP 1.110), a modified version of ISO 10110. Among other slight differences, it is likely to permit the (optional) use of military standards.