[atlas] Understanding participating probes and probe requests

Hi,

I'm currently looking at measurement metadata and am a bit confused about the different ways of getting the number of probes participating in a measurement and the number of probes requested by the user.

I'd like to know how to...
  1. get the number of probes _currently_ participating in a measurement (for ongoing measurements)
  2. the number of probes that participated when the measurement finished (for stopped measurements)
  3. the number of probes a user requested over the lifetime of a measurement

The default response to /measurements returns a participant_count and a probes_requested value. However, there are also the optional fields current_probes and participation_requests and these do not add up.

For example, this [0][1] measurement (not mine) has a participant_count of 0 (showing as "Actually Participating: None") in the web interface, but one probe listed in current_probes, which shows up in the "Latest Results" list and is still performing measurements (at least while writing this).
So it seems like the current_probes list is more accurate to get the number of probes _currently_ (or when the measurement finished) participating in a measurement?

Similarly, there are 35 probes_requested, which equals the sum of "requested" probes from the participation_requests, however, some request are actually "remove" actions, which should not be included in this count?

Any hints on how to interpret these fields?

I think the requested probes and participation requests are more a problem for long-running measurements, but the participant count is sometimes weird for one-offs as well.

Thanks,
Malte

[0] https://atlas.ripe.net/measurements/67903255
[1] https://atlas.ripe.net/api/v2/measurements/67903255?optional_fields=current_probes,participation_requests
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