Weird stroke rate in log ?

[JaapvanE]

I think recently I've see some crazy numbers on the PM5 for very short intervals (I think I was on 250m intervals). The SR was very off at interval start and it progressively went to the "right" value.

Okay,

I'm officially intregued now.

I downloaded the csv file from the concept2 site, which contains the raw underlying data from the Concept2 from the PM5. As expected based on the RowsAndAll data, for the segment 2000 to 2500 meters:

• I did 47 strokes to get from 2001.3 to 2500.3 meters, which took 2:12.6, which results in 21.26 SPM
• The average of the instantaneous stroke rates (which is recorded in whole numbers) is 21.16 SPM
• Based on the timestamp, I calculated the average time between strokes, which is 2.82 seconds, or 21.28 SPM

At the segment between 14000 and 14500 meters (I made a mistake in my previous post, selecting the wrong split segment. In this segment in the RowsAndAll data, the SPM hit the 22.5 twice, and the rest was below the 22.5 SPM), I see the following in the Concept2 data:

• I did 50 strokes to get from 14000.5 to 14507.6 meters, which took 2:14.5, which results in 22.30 SPM
• The average of the instantaneous stroke rates (which is recorded in whole numbers) is 22.29 SPM
• Based on the timestamp, I calculated the average time between strokes, which is 2.68 seconds, or 22.32 SPM

So when calculated by hand/Excel, the SPM data per split from Concept2 is just wrong.....

PS: I realize that the SPM numbers all should be rounded a bit further to single or no digit precission, however to illustrate the closeness of these numbers I wanted less rounding in these numbers, as it shows it isn't even close to a boundary like a *.5 value...

[JaapvanE]

Well, as when counting strokes your max absolute error is +/- 1 (EDIT: only -1 in fact) stroke per interval, usual interval lengths (multiple minutes) wouldn't suffer too much.

I think it is a maximum of almost two: at the begin a 0.99 stroke can be excluded as it is partially in the previous split, and at the end a 0.99 stroke. With splits of 500 meters and a DPS around 10 meters, that is the difference between 50 and 48 strokes: when using a 2:00 split, that is the difference between 25 and 24 SPM....

[jamesg]

SPM data per split from Concept2 is just wrong

All data is wrong; the question is by how much.

At stroke 1 there is no data from non existent stroke 0, so stroke time 1 can only be catch to finish. Which could be 0.7 to 1s, according to length and strength, so 60 to 85.

In JustRow I saw just now 65, 25, 21, as expected.

What's the time unit in the C2 clocks?

[JaapvanE]

What's the time unit in the C2 clocks?

I don't know, but drivetime is reported in a 10 milisecond (ms) precission, which seems to match OpenRowingMonitors calculation in microseconds precission (us). And their end-time is in 100 ms precission (the tenth of a second).

[HornetMaX]

Could this be an issue we've seen before with heartrate, where the average HR isn't the average at all, but the last measured value?

Just tried this: 60min session with 10 min splits (splits, not intervals). Only did the 1st 10min at SR19 except last 30secs at SR32.
Logbook says SR for 1st split is 19. Link here.

So no, it doesn't seem to log the last SR for a split (didn't try for an interval but ...).

[Citroen]

What's the time unit in the C2 clocks?

They're accurate to 0.1s.

[JaapvanE]

What's the time unit in the C2 clocks?

They're accurate to 0.1s.

A PM5 reports a drivetime that is accurate to 0.01s, so internally they must be more accurate than 0.1s