Opthalmic Frames
Measurements & Markings

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Box System of Measurement

Frames may be measured using either one of two systems, the Datum System or the Box system.

When measuring an eye size using the datum system, an imaginary line is drawn through the middle of the eyewe both in the horizontal and vertical planes. The length of those lines correspond to the horizontal and vertical measurements of the eyewire. Given a shape such as that illustrated above, it is easy to see how inconsistencies in measurement can result using this system.

The box system is more accurate and more widely used in the optical industry today. In this system an imaginary box is drawn

iraround the area to be measured. The distance between opposite, parallel sides of the box determine the length of the distance being measured. This system yields accurate measurements even with unusual shapes.