Model: TI-2511Battery: 4 x AA alkalineAdapter: AC9900/eYear: 1974Chip: TMS0119Info: 1 version
Model: TI-2550Battery: 3*AA NiCd or 4*AA Alkaline Adapter: AC9130 or AC9120Year: 1974Chip: TMS0601Info: Released one year after the legendary TI-2500, the first with a lens display (like bubbles)
Model: TI-2550 IIBattery: 2 AA or BP2Adapter: Year: 1976Chip: TMS1071Info:
Model: TI-2550 IIIBattery: BP3Adapter: AC9130AYear: 1976Chip: TMS1043Info:
Model: TI-2550 IVBattery: BP4Adapter: AC9900/HYear: 1979Chip: TMC1981,TMC0999Info:
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