|Name and Model Number||Proell Pocket Calculator|
|Country of Origin||Germany|
|Date of Manufacture||~1901|
|Front Scales||Base scale 15cm x 10cm Scale 1-10 split into 10 rows. sliding scale 15cm x 10cm as base but inverted.|
|Back Scales||Basic instructions|
|Scale Length||Length of calculating scale 120cm|
|Type of Rule||Other|
|Construction||Card base scale & celluloid sliding scale|
|Area of Use||Generic|
|Comment||A grid iron rule.
Manufactured in Germany, John J Griffin was the Great Britain agent,
GB Patent No. 2516 1901. Complete with slip case and instruction booklet.
|Donor||Collection of Peter Fox|
|RR||= Rare -- 1 of 25 collectors has one; it may take a year to find an example in the marketplace.|
|RRR||= Very rare -- only very few known to collectors; may take several years before one comes up for sale.|
|RRRR||= Extremely rare -- a museum piece; unlikely that an example will ever come up for sale.|