This is the unit as illustrated. It will work with any Polar coded or uncoded wrist unit like the A1, A3, F1, F4, F5, S610, S720i etc. Coded transmission reduces the risk of cross-talking in a crowded area, so training computer finds your horse’s heart rate and not someone else’s. The heart generates an electrical signal that can be measured on the skin. The Polar Equine T52H coded transmitter contains two electrodes to detect the electrical signal of every heart beat and sends this information continuously and wirelessly to the training computer. The electrodes are mounted on a sealed transmitter that is attached to the saddle. Putting the transmitter into place is extremely simple: the + electrode is first placed under the saddlecloth, the – electrode is then fixed to the saddle girth, and finally the transmitter is fixed to the saddle.