By appeal of the Free Electors party, a first repsonse of the internal service provider it@M references savings of more than 11.5 M Euros. The reasoning is based on three scenarios: One solution based entirely on Microsoft products, one mixture of WIndows and Open Office, and the actual costs of the current LiMux project.
The savings is primarily based on calculating software licenses, and they contribute almost seven million Euro in the Microsoft pure-play scenario. In addition, the statement refers to a required Hardware Upgrade that cause an additional spend of about five million Euros. The experts, however, do not balance the savings calculation with discounts typical for such procurements, neither do they account for hardware refresh that would be necessary for any reason from time to time. This way of calculation naturally bring up the question what such comparison is worth when 75% of the savings can be debated.
When setting up a rationalization for platform decisions, you should always be careful with internal assessments, to avoid the impression of being partial.
If numbers are not evident - like in this case - your reasoning might backfire: Instead of supporting your technology direction, they generate doubt about your own expertise and capability which might create continuous re-iteration of the topic!