A hexagesimal format minute has a maximum of 59 seconds (just like an ordinary minute), so the largest fractional seconds value you'd see in a mm.ss expression is .59. In a decimal format such as you assumed, though, it can go up to .99.

The advantage of the hexagesimal format is that there is a 1:1 relationship between the fractional and actual seconds value. With a decimal format, only one-third of the seconds can be expressed exactly with a fixed number of decimal places.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]