Make Unknown
Model Gunter scale
1. Before slide rules were invented Gunter's scales were used. These were initially a single scale with the marks on the scale being proportionasl to logarithms. To use them it necessary to use a pair of dividers to mark of distances and to add them for multiplication or subtract them for division.
2. To prevent the dividers making permanent holes in the wood at frequently used points small, circular brass inserts were sometimes used. These can be seen in the detailed image of the special scale below.
3. Whilst a basic Gunter had just one scale this has several. At the top there is a scale of inches and one of 100ths of a foot. Below that is a scale of "chords". These appear to be equivalent to the present day word "degrees" but I can find no reference to this. Further down there is a sin(e) and a tan(gent) scale. I would have expected the VS scale to be versine (versed sine from the latin to turn) but the numbers do not appear to appropriate.
4. The rule also has a number of special scales. The one shown relates to the relationship in hours from the meridian and degrees; 6 hours,  a quarter of day, being equivalent to 90 degrees, a quarter of a circle. On this scale one would expect the 45 to align with 3 hours but it does not do so exactly. Whether this represents some complex navigational correction or is simply an error I do not know.
5. The reverse of the rule has a number of scales arranged arranged at different distances, possibly for scaling from maps.

This rule is from the collection of M Taylor.

Front view

Detail front left
023-gunter-02.jpg (54794 bytes)

Detail front right
023-gunter-03.jpg (63470 bytes)

Detail - special scale
023-gunter-04.jpg (23720 bytes)

Back view
023-gunter-05.jpg (60274 bytes)

Detail - back left
023-gunter-06.jpg (46521 bytes)

Detail - back right
023-gunter-07.jpg (63713 bytes)

Manufacturing date Possibly 19th century
Length 12"
Material Boxwood
Scales See above
Cursor None