Scientific Instruments Co. (SIC)

Scientific Instruments Co. also made rules rebranded as Star.

No. 120-D Professional, 1963 (1 of 2)

A sturdy and powerful circular rule, measuring 4.25" in diameter. Unusually for circular rules, the main scales (K,A,D,C,B) run counter-clockwise from the 6 o'clock position.

It's also unusual that the main cursor sports two hairlines, a large one that runs the full radius of the side and one small one over just the A scale. When the small one is set to 1.0 on A, the full one is at 1.27 on A.

Now 1.27 ~= 4/pi, so if the large hairline is set at d on D, the small cursor yield pi * (d*d) / 4. This may look strange, but if we let r = d / 2 it becomes clear: pi * (d*d) / 4 = pi * (r*r) = the area of a circle of diameter d. Cute, eh? This slide rule calculates the area of a circle in one step!

This example was missing some of it's original hub hardware - a couple compression washers and a custom screw. I fashioned something to replace them, but short of buying another incomplete rule, I don't think I'll ever find another one of those screws.

No. 120-D Professional, 1963 (2 of 2)

This next 120-D was gifted to my collection by the son-in-law of Donald Lee Hall, who used it as an Assistant Highway Engineer for CalTrans in the 1960s.

After a little cleanup, it's in great condition! I'm thankful for it.

Interestingly, this 120-D is every so slightly different than the one above. On the reverse side (above right and below left) the word "Japan" is on the opposite side from the rest of the text.

No. 1610-D

At 5" in diameter, the 1610-D is basically a 120-D to which SIC added LL0, LL1, LL2 and LL3 scales on one side, and their reciprocals on the other.

No. 120

Back to 4.25" diameter, this is the 120-D's less powerful sibling. Where the 120-D has a rotating disk on both sides, the reverse of the 120 is static.