Gym routines and hours on the trainer aside, truly improving on the bike can be hard to quantify when you don't have the data. Power Meters provide us with sound, tangible numbers that show us where we're excelling, and where we have room to push harder -- the only problem is the often wallet-draining price tag that goes along with them. Quarq aims to mitigate this issue with its DFour Power Meter Alloy Crank Arms, which drop the pricey carbon alternative for trusty aluminum, simultaneously knocking the price down a few pegs to be a bit more pocket friendly. Despite its alloy shell, the internals work the same as its sibling. The DFour is, essentially, the DZero model but with one fewer chainring bolts and a bolt circle diameter (BCD) that fits Shimano's latest generation of 11-speed road chainrings, specifically Dura-Ace 9000, Ultegra 6800, and 105 5800. That means that, with the exception of the latest Dura-Ace 9100, the DFour is compatible with every 11-speed road drivetrain Shimano has engineered to date, so fans of the Japanese company aren't relegated to choosing between more expensive or less accurate power meter options. Except for that compatibility difference, the DFour incorporates every piece of technology Quarq crams into the DZero. Chief among these is the power meter itself, which saw a healthy amount of retooling. Overall, Quarq claims that "150 documented improvements" inform the evolution from the previous models to DFour, but the most important is to the heart of the meter itself: the strain gauges and measurement circuitry. It still incorporates five strain gauges strategically placed throughout the spider in order to measure the Newton meters you're throwing into the pedals. It's also still got the same claimed accuracy of +/- 1. 5%, so its numbers are 0. 5% more accurate than most meters, but the new design requires less correction in order to maintain accuracy in drastic temperature changes. Fewer corrections mean the DFour also better rati...