PowerTap SL - Manual (Page 31)

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Some of the more sneaky of you will try calculating power/heart rate for just one ride to see how cardiac fatigue
might be affecting your ride. You'll do this by running the .CSV file in Excel and calculating the factor for each
record. Then you'll replace the calculated column for the existing, say, Torque column. This is very naughty. You
need to know that as soon as you import that data into your database, it will affect your entire database history until
you delete the ride. If you want to try such experiments, it's best to import such adulterated data into a separate
rider name.
D Da atta ab ba as se e M Ma an na ag ge em me en ntt
As long as you are keeping all the raw data (.CSV) files, you can always start over by importing the files again.
Remember that you can always delete a ride and rider from the database to start over.
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There are two issues here, data inconsistency and time differences. First the display on the PowerTap CPU has a 3
sample running average. This 3 sample average is used for displaying averages
and maximums on the PowerTap computer display. This reduces the "jumpiness" of the numbers and makes it easi-
er to use while riding.
The data saved for download is raw, exactly as it is sent to the hub.
In the CPU set up mode (press MODE and SELECT buttons simultaneously until you see 'SETUP') you can select 1
or 2 sample recording. If you select 1 the data is sent to the CPU from the hub at 1-second intervals. The 1-sec-
ond mode will save every data point sent from the hub. If you select 2 the data is sent to the CPU at 2-second
intervals. The 2-second mode will in effect save only every other data point sent from the hub. Therefore in the 2-
second mode Maximums can be missed.
So between the averaging and the save rate the data download will be different. In the 1-second mode the down-
load data is always most accurate.
The second issue is time differences. The data points used for display on the CPU may not coincide perfectly with
what is stored to memory. There can be up to a 1-sample (or 1-second) loss at the start and stop of a download
file. If the CPU is in 2-second mode this max time error (2-seconds at the start and/or stop) can be as much as 4-
seconds off.
The individual raw data records written to memory are extremely accurate. In fact the data has been proven in lab-
oratory testing to be accurate to +/- 1.5%. This means the data downloaded to the Link accurately represents what
was happening on your bike second by second. How we repackage the data, to make it useable does not affect or
detract from its accuracy - it's just making it more user friendly.
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