SRM pioneered the crank-based power meter way back in 1987, and has continued to set the standard by which the rest of the industry follows ever since. The SRM power meter boasts an exceptionally precise accuracy window of less than one percent, making it the virtually unassailable bench mark for measuring power in research settings. Paired with Campagnolo's carbon fiber crank arms, the SRM Campagnolo 4-Bolt Powermeter Crankset delivers impeccable power transfer, accurate measurement, and a dash of Campy style. But don't take our word for it; just watch the final two mountain stages of 2016's Giro to see what a guy like Nibali can do with this here crank apparatus.
SRM measures torque with four measuring bridges along the spider in the heart of the crankset to capture data at the transfer point between the crank arm and chainring, which is then plugged into an equation along with pedal velocity to determine power output. With a less than +/-1% accuracy window and a reading range of zero to 4,200 watts, rest assured that you're getting the right readings to keep your training on track.
Although the crankset looks strikingly similar to Campagnolo's standard Record crank, it does have some differences. SRM worked with Campagnolo to develop a custom carbon fiber crank arm that integrates seamlessly with the SRM spider. Despite this necessary difference, the SRM Campagnolo crankset still features the renowned Cult bearings, which Campy claims enjoy 3.5 watts of improved pedal efficiency with each pedal stroke and the lowest coefficient of friction available courtesy of the perfection of ceramic bearings and Campy's top-tier races. The crank arms are essentially Record crank arms minus the Record spider, so they're made with the same Ultra-Hollow technology to deliver exceptionally light weight yet impeccably stiff power transfer.
The SRM Campagnolo 4-Bolt Powermeter Crankset was designed to pair with SRM's separately sold Powercontrol head units, but is also compatible with other ANT+ head units to record data and save files for review on your favorite training data analysis software. While we can't in good conscience recommend taking these crank arms (or any other power meter) swimming, SRM specifies that the system is sealed to prevent water or debris from working its way in and gunking things up.
A side effect of this closed system is that the battery is not accessible to the user, which necessitates sending the unit to SRM for replacement when it runs out. The good news is that its claimed battery life of 1900 hours means even the most prolific cyclist won't have to worry about this minor inconvenience more than about once every few years.