Weston Ranger 9 Universal Exposure Meter Model 348. 1966, USA manufacture.
A close up of the calculator dial showing a model where the outer multiple pointer dial has been over-pasted with an overlay designed for use with the Ansel Adams Zone System. The multiple pointers on the outer dial have been moved to the outer edge and the Exposure Value (EV) scale has been overlaid with a sequence of ten grey tones which correspond to Adams' Zone System for determining exposure.
This detail from the Ranger 9 instruction book illustrates the push-fit Invercone.
Below is an artist's impression of the Zone System overlay as it appears in the manual. This must have been published prior to the actual overlay becoming available, as the actual crescent stick-on panel is very different in design.