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Vertex Distance Conversion Disc
MANUFACTURING AND DISPENSING EQUIPMENT
slide rule
Rayner
Europe: United Kingdom, England, London W1
Mid 20th c.
cardboard
overall: 178 mm x 178 mm
2012.152
MANUFACTURING AND DISPENSING EQUIPMENT
slide rule
Rayner
Europe: United Kingdom, England, London W1
Mid 20th c.
cardboard
overall: 178 mm x 178 mm
Conversion slide rule for calculating vertex distance of lens prescriptions, comprising a square piece of cardboard with rotating disc and millimetre scales for plus and minus lenses. Directions for use printed on the reverse.
2012.152
Gift of Mr David Randall, FCOptom, 2011