The DFour Power Meter Spider is for cyclists already equipped with a Quarq Elsa RS eight-bolt power meter who are interested in the improved functionality of Quarq's latest, DZERO technology. This smart spider lets you keep the components from Quarq (spindle and crank arms) and Shimano (chainrings) that you're currently using, letting you upgrade to more precise power data without forcing you to toss perfectly a perfectly good crank chassis. If you've got the Prime crank and want to up your training/competitive game, then the upgrade makes obvious sense. If you're already rocking a previous generation of Quarq's 8-bolt powermeter spider, then the reasons are, admittedly, less compelling, and are defined by the internal changes Quarq made to the meter. Of these, the most important is to the heart of the meter itself: the strain gauges and measurement circuitry. The new design requires less correction in order to maintain accuracy in drastic temperature changes. Fewer corrections mean the DZero also better rations battery life than Quarq's previous power meter models, though when the battery does go out, you can still change it without tools or having to ship the whole thing to the manufacturer. It still incorporates five strain gauges strategically placed throughout the spider, and it's also still got the same claimed accuracy of +/- 1. 5%, so its numbers are 0. 5% more accurate than most meters. DZero's accuracy is further boosted by the return of Quarq's 10k dynamic temperature compensation technology, which alleviates the need for constant, mid-race zeroings in variable conditions. Even if it's just coasting for a few seconds or toggling through your head unit to the proper option, it can still be the difference between winning and losing. It's also obnoxious as hell. The DZero is equipped with an auto-adjust schedule based on a constellation of around 10,000 data points that chart how the unit responds to temperatures ranging from zero to 130 degrees Fahre...