The following paragraph from a SG Sensortechnik press release is said to explain all, but it must have been through a wonky Babelfish translation.
"Heart of the system is the sensor explained as a pedal-crank bearing. By the pedal step the axle of the sensor becomes minimally tordiert. The Torsion of the axle becomes by the high-resolution, already in the thousandth degree an area attractive measuring principle ergomoâ measured."
Hmm, yes, clear as mud.
What SG Sensortechnik lacks in translation skills it makes up in sheer cleverness. The Ergomo system is not a cheap copy of the SRM system (which, anyway, is well covered with patents), it's a wholly different solution to the problem of measuring a cyclist's power output.
Other power measuring systems include the Power Tap Pro and the Polar Power 720i.
Power equals strength times cadence, measured in watts.
Heart monitoring alone does not tell you how your actual performance is improving, it just tells you how hard your heart is working. A power meter measures your rate of work (power), and analyzes your efficiency by allowing you to compare heart rate data to power output to your cadence and finally to your speed.
Ergomo consists of a bottom bracket sensor, a bicycle computer that can measure speed, cadence and other normal computer functions, and PC software for analysing the data spewed out by the power sensor.
The system was developed by engineer Siegfried Gerlitzki and tested by US cycling coach Hunter Allen.
Gerlitzki said the measuring exactness of the system is in the region of 98.5 - 99 percent.
The bottom bracket sensor weighs almost the same as standard BBs and is available for tapered square or Shimano OctaLink double or triple cranks. There's no need for special cranks, wheels or hubs.
The SRM system costs about $2300. The Ergomo system will retail for $1479.