One shift, checked two ways
A shift from 9:15 to 17:52 has a duration of 8 hours 37 minutes, which the time duration calculator also reports directly as 8.6167 decimal hours. Taking that same "8:37" result and running it independently through the decimal hours converter gives exactly 8.6167 — the identical figure, computed a second, completely separate way.
Why the two calculations necessarily agree
Both are doing the same underlying arithmetic — converting 37 minutes to a fraction of an hour (37 ÷ 60 ≈ 0.6167) and adding it to the whole 8 hours. One calculator does this as an internal step while computing the duration; the other does it as its entire, standalone job. Feeding one calculator's output into the other doesn't introduce any new computation, just confirms the same math twice.
Why this matters for trusting a payroll figure
For someone processing payroll from a shift's start and end times, seeing the same decimal figure whether it comes directly from the duration calculator or via a separate H:MM-to- decimal conversion is a useful sanity check — it confirms the number being multiplied by an hourly rate is correct, not an artifact of a formatting quirk in one particular tool.
When you'd actually want each calculator separately
Use the duration calculator when starting from two clock times. Use the decimal hours converter when starting from an H:MM figure that's already been recorded somewhere else (like a timesheet entry) and needs converting for payroll — both roads lead to the same number when they describe the same span of time.