To convert Excel to TM1 dates subtract 21916

[John Hammond]

Given its integration with Excel it seems a strange choice that the base date chosen for TM1 dates is 01/01/1960.

Is there any logic for this or is it just the founder of TM1's birthday or when Denmark won the world chess championship or something like that.

Any views appreciated.

[Steve Rowe]

Maybe the base spreadsheet sytem for TM1 was Lotus 123 and it comes from there?

[Alan Kirk]

Maybe the base spreadsheet sytem for TM1 was Lotus 123 and it comes from there?

Nope. Lotus 123 also used 1/1/1900. That's actually where Excel inherited its "1900 is a leap year" bug from. The Excel designers knew it was wrong but they had to adopt it anyway or risk breaking compatibility with Lotus. (Which mattered, back then.)

If I had to make a guess it would be because the original versions of TM1 only supported 2 digit years; I think that the 4 digit kind came in around 8.3 or 8.4 from memory. Date calculations using the first decades of the 20th century would be irrelevant for most purposes, whereas back in the mid 90's when TM1 first flowered you'd run out of dates pretty quickly had you used 1900 as your starting point. A start date of 1960 would give you the ability to calculate out to 2059, a far more useful range. But any start date, even 1/1/1900, is arbitrary.

(Edit: I just did a search of the release notes and it was 8.4. And let's not forget that the Macintosh uses 1/1/1904 for its arbitrary date. Might have been Steve Jobs' birthday, but I doubt it...)