The observed rate is the displayed count ledger divided by the full clock interval, before correcting for detector dead time. The fraction is exact for the stated count and clock duration; measured rates carry clock calibration error, missed counts, background subtraction choices, dead-time bias, and counting-statistics uncertainty.
The displayed observed rate is the exact count/time ratio. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.