HP -01 Owner's Manual page 87

Typically, the time display is divided into three parts. If a second colon is pressed, the time
interval is interpreted as HH:MM:SS. If the decimal point is pressed, the time interval is assumed
to be MM:SS.CC.
Press Display Comments
In either format, the digits to the right of the colon occupy a two-digit field. As other digits take
their place, numbers in the field shift to the left then disappear, leaving only the last two digits.
Hence, the keystroke sequence @ @ @ © @ @ produces a displayed resultof 00 : & |
That's why you can correct time entry errors without clearing and re-entering the entire number
again.
Operational Description 85