1. Mannheim type single sided student rule.
2. At first I thought that this rule had been taken apart at some time and re-assembled with pieces missing but on examination it is very similar to the Acu-Math 1311 which is also constructed in a similar fashion.
3. The Cursor is strange as well. I can't work out if it came this way or it has been modified. The cursor is the same as the Acu-Math 1311 but it only has one plastic cursor plate. The screw holes have been plugged with metal inserts. It looks like the factory decided that the simplex rule did not need a second plastic face.
4. This rule appears to be an earlier version of the two other examples I have of the 511. I have added all of these to the collection as they are all different and show the progression of the model. The others are listed here as Acu-Math 511 (2) and Acu-Math 511 (3) (Yellow).

Brand	ACU-MATH
Model	No. 511 - Student Mannheim
Country of Manufacture	USA
Scales Front	S, K, A [B, CI, C] D, L, T
Scales Back	Equivalents tables
Number of Scales	9
Slide Rule Materials	Metal core, plastic faces with metal end pieces on back only. Metal core looks like magnesium
Cursor Materials	Plastic
Cursor Lines	1 Front
Scale Length	25 cm
Length	31.7 cm
Width	3.9 cm
Condition	Fair.
Documentation
Accessories	Vinyl Case