The City Frame & Lens Rule (sometimes known as the Serelo Rule) was designed at the City University, London. This rule can measure the following aspects of frame and lens parameters: 

·          Angle of crest 

·          Angle of let-back 

·          Angle of sides 

·          Downward angle of drop

·          Frontal angle of pad 

·          Inward angle of drop

·          Splay angle of pad 

·          Vertical angle of pad

·          Apical radius 

·          Boxed lens size and centres

·          Bridge width, crest and height 

·          Distance between centres 

·          Distance between lenses 

·          Distance between pad centres and lenses 

·          Distance between pad centres and tops

·          Distance between rims 

·          Frame head width 

·          Frame temple width

·          Front to bend 

·          Frontal width 

·          Height of pad centres and tops

·          Inset of pad centre 

·          Joint height 

·          Joint size 

·          Length of drop 

·          Length to bend 

·          Length to tangent 

·          Projection of bridge 

·          Lens insets, progression heights and segment positions

·          Segment diameters height and size 

Supplied with an illustrated manual.