The resolution of the time-of-day clock is one microsecond, and the clock is incremented by adding a one in bit
position 51 every microsecond.
The program is not alerted to the overflow as the clock
value changes from a large positive value to a large negative
value because of a carry from bit position 1 into bit
position O. No interruption condition is generated as a
result of the overflow. When incrementing the clock causes
a carry to be propagated out of bit position 0, the carry is
ignored, and counting continues from zero on.