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The 4iiii Precision left-side power meter adds just 9-10g to a crank (Image credit: Ben Delaney/Immediate Media)

This article originally appeared on BikeRadar

So is this left-only power meter accurate? In my testing, I found the answer to be yes, mostly. I have found that for tempo efforts and above, my left/right balance is usually between 50/50 and 49/51. At easier, just-toodling-along paces, the left/right balance can vary more. Cycling coaches say this is the case for most people. For me, I'm not really concerned with exact wattage numbers when doing an easy ride or recovery between efforts; I am interest in accuracy when doing intervals. For this purpose, I found the 4iiii Precision to be a good training tool for the price.

I ran the 4iiii Precision alongside an SRM and a PowerTap, which have tracked closely to each other for years and are the closest thing I have to a gold standard for testing Shimano crank-based meters, plus a set of Garmin Vector pedal-based power meters, for left-right reference. (Unfortunately the SRM battery gave out partway through testing and, revealing a flaw of the very expensive unit, required returning to the manufacturer for recharging. So, some of the charts here show only PowerTap and not SRM.)

When testing power meters I overlay the 1-second and 30-second data to get both the forest and the tree view. I'm not too worried about one meter reading slightly higher than another or having a slight lag, but I do worry when one meter diverges greatly from the trends that the other meters show. In my experience, for example, Garmin Vector pedals are sometimes good and track well against SRM, PowerTap and Quarq, but then sometimes the data just wanders for no explicable reason.

Given the water-entry problems that many of the early Stages meters faced with the battery housing, I tried to abuse the 4iiii housing by blasting it with a powerwasher, and using various types of sudsy solvents. It held out water without issue. (The same can't be said for one of the Garmin Vector S pods, which popped open like clamshell after a sudsy wash. This didn't affect measurement, but did require some duct tape...)

When it launched, Stages was unique for being a left-side-only crank based meter. This design makes it more affordable, less complex and easier to fit. Power is measured with strain gauges factory-bonded to a left crank, doubled and then sent to a head unit via ANT+ to a computer or Bluetooth to a smartphone app. The new housing has addressed the water-seepage issue that plagued some of the initial units.
Read the full Stages Dura-Ace 9000 power meter review

Pioneer offers a unique power meter configuration: the dual-sided meter can be split into two functional one-sided meters. Further, when used as a dual-sided meter, Pioneer can give you what the company calls force vector measurements, showing where and in what direction power is being applied at 12 points along the pedal stroke. More pertinent to the 4iiii Precision, Pioneer is selling its left-sided meter for US$629, with the option to upgrade to the dual-side down the road.