Commodore US*10 Desktop Calculator
The Commodore US*10 is one of a fairly large line of US*x machines made by commodore in the 1972 through 1975 timeframe. The machines distinguished themselves by low-cost, simple construction, and basic functionality. The US*10 is virtually a clone of the US*8, with the only difference being that the US*10 provides a ten digit capacity with the US*8 providing eight.
Internally, the machines are also nearly identical. The circuit board layout is very close to the same, with identical keyboards, power supply circuitry, and clock generator. The US*10 uses a Texas Instruments TMS0106 single chip LSI (versus the TMS0103 in the US*8), and has a 11-digit Burroughs Panaplex panel (versus 9-digits on the US*8's display panel). The display driver circuitry is identical between the two machines, with a couple of additional digit drivers for the additional digits that the US*10 has over the US*8.
The display uses a seven segment digit arrangement with the left-most digit in the display panel used only for sign (-) and error/overflow indication.
The machine uses adding-machine style logic for addition and subtraction, with "+=" and "-=" keys for accumulating sums and differences. Multiplication and division work as expected, with the "+=" key used for calculating the products or quotients. A slide switch selects fixed decimal point locations at 2, 3, or 4 digits behind the decimal point, or full floating decimal modes. A push-on/push-off "K" key turns on constant mode, allowing a constant value for multiplication or division.
This particular US*10 was built in the mid-part of 1972, from the date code on the LSI. The machine is about average in speed for an early single-chip four-banger, with all nine's divided by one taking about 1/3 of a second to complete. The displays are not blanked during operations, and jump about a bit on the longer calculations.