Price information in many cases comes from Büromaschinen Lexikon, an important yearly book describing all relevant office equipment available in that year in Germany. A manufacturer or product not being mentioned in this book was considered to be commercially very unwise.
Prices were given in Deutche Marken (DM). With available historical currency information this price was converted to Dutch guilders. In some cases price information could be confirmed with Dutch or American adverts.
Currency information comes from several sources on the internet, among others:
With information about salaries the price in Dutch guilders has been “converted” to the number of months or weeks it would take somebody with an average income to pay for a calculator. Salary information comes from:
Of course there is a lot of inaccuracy in this multi-step method, but I nevertheless hope that it gives a good impression how very expensive calculators were in the years before the early 70’s and how fast they became cheaper and cheaper in the years afterwards.
Actual prices in DM or Dutch guilders (where possible regarding the year of introduction) can be found in the machine’s detailed description.
Price information in months income of a worker with a regular salary