A cumulative number needs a time boundary
A phone's per-application data counter can help investigate viewing usage, but first identify the period it covers. Apple documents application-level cellular statistics and a reset control. Do not assume a displayed cumulative total describes the last programme or matches the carrier's billing period. Preserve the existing record before resetting it.
Check which mobile line is selected when the device uses more than one. Record the application, displayed period or reset reference and units. A phone streaming directly and a television using the phone's hotspot can place usage in different reporting contexts, so identify the actual viewing route as well.
A hypothetical short observation
Suppose an application's cellular counter reads 100 MB before a controlled authorised sample and 340 MB afterward. The displayed increase is 240 MB over that observation. That is more specific than assigning the full 340 MB to the sample. It still reflects the application's activity during the interval, which can include requests beyond the visible picture.
Write the start and end times and avoid unrelated activity in the same application during the sample. Note any change between Wi-Fi and mobile data. Do not repeatedly stream a long programme merely to make the number easier to see on a limited allowance. A short deliberate observation and the actual carrier record are more useful than an expensive uncontrolled experiment.
If you reset statistics for a future observation, save the previous period first and note the reset time. Resetting a device counter does not restore a carrier allowance or remove charges. Apple directs users to the carrier for the most accurate usage for the current period; the local counter is a practical diagnostic, not the billing authority.
Keep measurement and planning separate
Use the observed application increase alongside the viewing duration when planning a comparable session. State the assumptions and allow for different quality selection or other activity. One short sample does not establish a fixed data rate for an entire catalogue, particularly where the player can change renditions.
A useful record contains the application, route, line, time window, before-and-after values and carrier context. It can support an informed viewing choice without claiming an exact bill from a screenshot. Keep this evidence separate from account-renewal terms: the media subscription price and mobile-network data use are different quantities.
Questions answered
Does a counter reset restore my mobile data allowance?
No. It changes the local statistics reference. The carrier controls the plan's allowance and billing record.
Can I assign the entire application total to the last film?
Not without the period and a baseline. Compare a defined interval and account for other application activity.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.