1. The early rule has no model number but seems identical to other early 40RKs. A later 40RK is provided for comparison..
2. Has Japanese characters on the well of stock which means "Large calculating device with special device for best reading - 92122 major patent number". (Thanks to Stéphane Guglielmo for translation).
3. The Japanese patent (92122) is dated 1912 and the British one (107 562, not shown in detailed view) is dated 1917.
4. In addition to "quot +1" and "prod-1" marking also has plus and minus signs on both ends of upper stock.
5. The later rule has similar scales plus a CI scale which in coloured red.
6. The trig scales use an almost identical type face. The window for these scales has a continuous vertical line, enabling the all scales to be used at either end of the rule.
7. A rule virtually identical to the 40RK was sold as model 1447 by  Frederick Post, USA.