The HP-55 (Merlin)


Introduced on the 1st of January 1975, discontinued begin 1977.

HP's sixth handheld calculator. Introduced as a low cost alternative for the HP-65. This model has no card reader and less instructions.



The color of the housing for this model differs from its family members. The housing is dark green.

This calculator has a lot of conversion functions, is programmable and has a build-in stopwatch (timer mode).

Serial number: 1509S09266

Backside instruction label

HP55 instruction label

This label is printed on thin metal sheet. The metal sheet is glued on the calculator. The backside label of this calculator is damaged in the upper corners. Below these corners two screws are located which need to be removed for opening the calculator. So, folded or punched label corners often betray that the calculator has been opened in the past (for repair?).


Books about the HP-55

HP published books with example programs for the HP-55 calculator.

Book HP-55 Book HP-55

See my HP-55 inside page if you are curious how this Classic model is build.


HP-55 related links: