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Texas Instruments TI-55

• Type: Semi-Algebraic Electronic Calculator
• Size: 6 x 3 inches / 15 x 8 cm
• Serial/Lot number: 4771352/ATA1281
• Date of Manufacture: March 1981

With case and instruction booklet. This is a basic scientific calculator, with basic statistical and linear analysis function. Hyperbolic functions and some unit conversions round out the features. While not billed as a programmable calculator, there are 32 programmable steps available. No branching support is provided. This is a feature mainly intended to let you program an arbitrary function and execute it with the [R/S] key.

This is one of the few TI calculators from this period that include the factorial function. Probably because the lack of branching support kept you from writing the function yourself.

Got this at an antique store in Seattle. The battery pack was toast, of course. Briefly considered restoring it, but then discovered the thing liked to eat 9 volts. So, I took it apart (It's all snapfit!) and soldered in a 9 volt clip. A little creative surgery on the outside of the battery pack casing turned the latter into a battery compartment cover and voila good as new. Don't know how long the battery will last though...