While this manual was written specifically for the H-model, it is generally applicable to the J-model as well. Also, most of the Controlled Key mechanism introduced on the E/F models remained unchanged with the H- and J-models. Even those looking to repair C-model machines and earlier, should find this manual useful.
These features required very careful engineering to co-exist with an already complex design that included the popular Controlled Key feature. The location of the clearing handle ("zero crank") had to moved forward more than 3 1/2" and the depth of the case itself extended almost 1/2" to accomodate the additional parts.
This recently discovered repair manual provides detailed instructions for repair and assembly of the H-model. One could only wish for a complete set of the special tools devised to assist the repairman in his work.
Take a look at this remarkable sectional view of an H-model.
The manual has been converted to html format by Andries De Man (ademan). This was a sizable task involving OCRing and hand editing the text, clipping and linking images, etc. Be sure to check out his website "Original Documents on the History of Calculators".
Finally, view this comprehensive, detailed manual on how to repair your H- or J-model Comptometer here