Allow the use of a bike cadence sensor on the boat deck between the slides together with a magnet on the seat of a racing boat (as is usually found in the stroke seat). The magnet passes over the sensor twice per stroke so need to divide the bike cadence by two. Also the drive and recovery are at different rates, so a bit of smoothing would be needed.
An app like this exists for the Suunto Ambit 2 although this one has no smoothing so likely fluctuates between two different rates in use
http://www.movescount.com/apps/app8245-Rowing_Stroke_Rate
A first order smoothing filter example below:
csr = Beta * cc/2 + (1-Beta) * psr
where:
csr, current stroke rate (displayed)
Beta, some constant to give optimal smoothing probably in the range 0.5-0.8.
cc, current reading from bike cadence sensor
psr, previous stroke rate (needs to be copied from current stroke rate when a new cc reading is available and prior to a new csr reading being calculated)
