For years I have calculated my bellows comp in my head for large format. I always enjoyed using my RB-67 partially because of the bully bellows comp scale which made the bellows factor calculation into a non-issue.
I wanted to improve my large format production rate as overall it is a notoriously slow process. This was one of the points where I saw that it could be better, not that it took me that long to figure out the factor but just having to go into math mode detracted from the experience of vision and visualization.
I have carried a legal size xerox of a ruler which I coated with packing tape on two sides for years. When backpacking a 4x5 I try to keep the kit light.
I decided to make a scale that was like the RB-67 scale which covered the lenses in my kit while giving me an inch ruler as well.
I immediately noticed that there were not many simple calculators for bellows extension on line so I fixed that...
I first made a 2 inch tall version and hindsight being 20:20 I decided I wanted it even smaller so I transformed it to make a 1 inch version. My Zone VI field camera has a 300 mm maximum bellows draw so my ruler ends in that range. The ruler is around 14 inches long.
Here is a zip with the two rulers, the 2 inch and the slightly more compressed 1 inch version.