Hand held electronic calculators were developed after mainframe electronic computers and there was a period when programmers and computer engineers had to use mechanical calculators to do their base 8 and base 16 calculations. A number of specialised calculators were developed for their use. The Hexadat is a base 16 mechanical pocket calculator that was made for computer engineers and programmers.

The Hexadat calculator was made by Addiator Gesellschaft of Germany and was used for base 16 addition and subtraction. Base 16 [hexadecimal or hex] is a positional numeral system. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen. For example, the hexadecimal number 2AF3 is equal, in decimal, to (2 × 16^{3}) + (10 × 16^{2}) + (15 × 16^{1}) + (3 × 16^{0}), or 10,995. Addiator patented the Hexadat on the 24th January 1967. It was manufactured from 1967 to some time in the early 1970s.

Other base 16 mechanical calculators in use at the time were the IBM Field Engineers Hexadecimal Adder, the Hex Adder and the Hexadaisy [see this post]. They were used during the period between the development of the electronic computer and the development of an electronic pocket calculator capable of hexadecimal arithmetic. Addiator Gesellschaft also made a base 8 calculator called the Octodat [see this post].

A complete unit is shown in the photographs below. The Hexadat is larger than most other addiators at 61 x 232 x 4 mm [2.4 x 9.1 x 0.2 inches]. The stylus has a ball point pen at its other end and is held in a loop in the zipped case. A label on the back of the Hexadat indicates that it was sold by Data Efficiency Limited of Hemel Hempstead, England.

The instruction sheet is dated October 1967.

The marks on the paperwork are artefacts of scanning.

The Addiator factory in Wolfach, Germany

In August 1977 Texas Instruments started selling the TI Programmer electronic pocket calculator. This performed the four basic arithmetical operations in decimal, hexadecimal and octal. It could also convert between base 10, base 16 and base 8. It cost $42.50 and killed the market for the Hexadat.