Referring to the datasheet below, does it mean the meter has a battery inside which can keep the internal clock alive for 30 seconds during the power outage? Another question, why does “control power 120 Vac and with maximum burden” have a different ride-through time (100ms vs. Sorry, unable to complete the action you requested.
Aftermarket power meters like Stages are bonded to inside of the crank arms. Stages (shown above) and 4iiii are the top aftermarket brands for add-on power meters, offering kits for most popular alloy (and some carbon) crank arm brands and models. They measure the power with a strain gauge that measures the deformation of the crankarm under power.
Why do you need a power meter?
An accurate power meter removes any doubts and replaces it with reliable data you can trust. Be confident in the knowledge that your fitness improvements are real. The spider-based power meters attach to AXS cranksets using a simple 8-bolt interface.
If you're Training (with a capital “T”) for real, it's probably best to put your power meter-equipped bike on the trainer and use that to track performance even if you're relying on your smart trainer to control resistance or online avatars.
How accurate is a power meter?
Most brands claim accuracy between +/- 1% for crank-based power meters, and the tolerance can go out as much as 2-3% for less expensive options. Asking how accurate you need it to be, though, is a bit of a trick question, because the real answer is “it doesn't matter” as long as you stick with the same one.
Spider-based power meters use Magic Zero technology to automatically calibrate the power meter for you, so you never need to worry about calibration! MagicZero works by continuously monitoring the torque signals from the strain gages as you ride, so you can focus on the road ahead.
If you have a smart trainer for indoor riding, capture power data straight from your power meter rather than your trainer to keep your data consistent from outside to inside. If you have a standard indoor trainer, your power meter will make it “smart” by allowing you to capture power and cadence data and transmit it to your bike computer.