1. This rule was designed for estimating the weight of cattle based on measurement. It included a tape measure and a circular slide rule.

2. The rule has the instructions on the back.

Directions First, take the length from the foremost upper corner of the shoulder-blade bone, in a straight line to the hinder-most point of the rump by the tail, and next the girth close behind the fore-legs. The measures carefully taken will, with the assistance of the circular sliding plate, tell the deadweight of the forequarters, either in the London Stone of 8 lbs., the country stone of 14 lbs., or the score of 20 lbs..

Example: suppose the length of the beast to be 5 foot 6 inches and the girth 6 foot 3 inches, turn the slide till the figure 8 with the * is over a 5 foot 6 inches on the inner circle, then look at 6 foot 3 inches on the outer slide, and over that on the outer circle will be found 90 stones. If the weight be required in stones of 14 lbs., turn the slide in the same manner till the figure 14 with the * is over the length, when the weight of 51 and a half stones will be found over the girth as before. Or if the score of 20 lbs. be required, turn the slide till the figure 20 with the * is over the length, when the weight will be found 36 score.

3. I can find no reference on the Internet to a "country stone" of 8 lbs.. There is however a reference to "butcher's stone" of 8 lbs (http://home.clara.net/brianp/weights.html). Given that this rule might have been used by butchers this is an interesting coincidence. Perhaps the sophisticated Londoners used the official 14 lb. stone whereas butchers from the country still used the 8 lb. stone.
 

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