by Janae Knott
Object: Vernier Caliper
A Vernier caliper is a linear measuring instrument, consisting primarily of a scaled rule and projecting arm with a sliding attachment,this forming a ‘jaw’ with the other projecting arm. The object measures internal and external distances with a high degree of precision.
Collection: The University of Toronto Scientific Instrument Collection
Maker: John Bull British Indicators Ltd.
Dimensions: (Box) Length: 32.5, Width: 20.2 cm, Height: 7cm.
Materials: Metal, plastic, 440 C grade stainless steel (The measurement jaw is also made out of stainless steel for strength)
Box: Wood, foam, plastic, and paper
Form and Fabrication:
The jaws are produced with stainless steel for corrosion resistance and strength. One has the ability to change the jaw and switch it for a jaw of another material. The scale is most likely aluminum or a metal of a similar grade, and the slide is made of plastic. Grooves along the slide allow it to glide on the scale, and this prevents jaw misalignment of disconnecting (when one moves it, it must lock into a groove to stay in position). The jaws must be attached in perfect alignment until precision is achieved. The dial indicates this instrument is used for accuracy, as it measures millimetres to 2 decimal places.
Provenance:
The object was donated by Cyril Gryfe to the University of Toronto.
Sources and Further Reading:
http://what-when-how.com/metrology/vernier-instruments-metrology/
“Method for Measuring Quantity of Bone”, A.N. Exton-Smith et al.
“Pattern of Development and Loss of Bone with Age”, A.N. Exton-Smith et al.
“Determination of the Amount of Bone in the Metacarpal”, C.I. Gryfe
Catalogue entry: 2017.ihpst.46