One of the first things everyone talks about regarding power meters is accuracy – and for good reason. What’s the point of training to a power meter that is not accurate? Well not much admittedly. However, there’s another important characteristic that your power meter should possess: consistency. In fact, consistency is arguably just as important as accuracy. In this article, we explore the power meter accuracy vs. consistency relationship and determine how these characteristics really go hand-in-hand.
Power Meter Accuracy vs. Consistency
Everyone knows the definition of accuracy. Put simply, does your power meter correctly measure the actual wattage you are generating? For example, if you are pedaling at 250 watts, does your power meter show a number close to 250? The closer to 250, the more accurate your power meter. Most direct force power meters claim an accuracy of +/- 2% or better. So in our example, if your power meter is truly accurate, it would registered between 245-255 watts.
Consistency refers to the repeatability of measurement. If your power meter reads 255 watts when you are actually producing 250 watts one day (2% high – an acceptable margin of error), does your power meter read 2% high the next day as well? If it does, your power meter is consistent. However, if it reads 2% high one day and 2% low the next, your power meter might be accurate (within 2%), but not consistent.
What’s More Important – Accuracy or Consistency?
Both! First let us make the argument for consistency.
When it comes to power measurement, it’s absolutely critical that your power meter is consistent from one day to the next. Imagine trying to use a bathroom scale that fluctuates by 10 lbs. from day to day. The results would be meaningless. At least in the short-term, you wouldn’t know if you were gaining or losing weight. Likewise, with an inconsistent power meter, you wouldn’t know if your power was increasing or decreasing. In order to properly use your power meter as a training tool, it must be consistent.
Sometimes you hear the argument that as long as it’s consistent, it doesn’t matter if it’s accurate. For example, the argument goes that it doesn’t really matter if your power meter reads 260 watts when you’re actually doing 250 watts. Rather, what matters is that you’re producing X watts more than you did a month ago at the same effort. And as long as your power meter is stable, reliable and consistent regardless of the conditions, you can accurately monitor your progress. This is logical enough, but…
But accuracy also matters. Here’s why…
Say you move on to a new power meter. Well, if your old power meter wasn’t accurate, it will make comparing your new data to your old difficult…if not impossible. Or maybe you train with two different power meters, each on a different bike. If they’re not both accurate, you won’t be able to compare your training data across your different bikes. In addition, sites such as Cycling Power Lab and Best Bike Split (that calculate race time estimates), depend on accurate power meter data. If your power data is incorrect, your time estimates will be wrong. Or maybe you want to compare yourself to the competition but analyzing key metrics such as your watts per kilograms at different durations. If you don’t have accurate power data, your comparisons will be skewed. As the saying goes…garbage in, garbage out.
Summary – Power Meter Accuracy vs. Consistency
So you really want a power meter that is both accurate as well as consistent. There is no reason you should settle for anything less. Do some research, buy a quality power meter, perform regular zero-offsets, and you should be good. As always, please contact us with any questions. We’re here to help.