Washington Sabatini’s circular reinforced concrete calculator #CivilEngineering #Vintage #Computing

This complicated circular slide rule comprises ten concentric aluminum rings covered with complicated scales and pointers. The rings are all movable except for the second largest; that one is fixed to the body of the device, as is the celluloid cursor overhanging the largest ring. The movable rings are rotated around the center of the device by use of the prominent crank handle that spans its radius.

Each ring carries a number of scales, and between one and three indices (the pink circles with a pointer) that point to the scale on the next larger ring. The multiplicity of scales and indices is due to the many types of concrete structures that can be calculated: rectangular beams, T beams, pillars, etc. Tiny icons reflecting the respective shapes tell you which calculation each index or scale is to be used for.

The identities of the various scales are given in a detailed fold out page in the manual. They represent loads, dimensions, moments, stresses, and other parameters that I would no doubt appreciate were I a civil engineer.

You can read all about this interesting device on Nathan’s Possibly Interesting Web Site Blog.