Following the calculation formula at http://www.vcalc.net/cu-date.htm I can't quite understand. The 1st example for Type I lists: 1951.5135 &
6.1620.

1951 I get, but why does the "6" in 6.1620 mean July if June is the 6th month of the year?

I try a Type I ser#28279 & get: 1955.4837 & 5.8044. Does this come out to late Jun 1955? Do we just ADD "ONE" the the month number as calculated?

Furthermore, I'd like to understand how to interpret the 4 digits to the right of the radix point. I've read almost everything, everywhere about the Curtas. Wonderful machines.. I'll buy my first rather soon & probably a 2nd after that.

I'm glad to be a part of the Curta Universe
Thanks in advance for any information you might have.

The Curta dating algorithm you refer to is just an estimate. It assumes that all Curtas were made in an even distribution over all the years they were manufactured. This is certainly not the case.

Nevertheless, many people do like to know what year their Curta was made. I often suggest that any formula be specified as a +/- 2 year accuracy.

6.1620 means July because January is the "zeroth" month...a date calculation between 0.0000 and 0.9999 is in January.

This is that same reason the second millenium "New Year" really began at midnight on January 1, 2001...not when everyone celebrated it one year earlier.