The extremely versatile Fairbanks Datum Rule can be used to take the majority of measurements relating to frame dispensing. It pre-dates the introduction of the boxed lens system but still remains a dependable and adaptable measurement gauge, used by dispensing opticians and optometrists throughout the UK.
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Measurements that can be taken include:
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Distance between lenses
Bridge width
Geometrical inset
Bridge height
Boxed lens size
Bridge width
Front angle of pad
Angle of side