You've been using your power meter for a number of rides now and have an ever evolving power curve. Its good to get familiar with what the numbers are at a few different durations. Popular lengths that people use are 30 seconds, 1 minute, 5, 10, 20, 30 and 1 hour. Get familiar with those numbers as this is the essence of what the power meter, as a tool, provides.
During the season I often go to
which is a fast training ride on a rolling course. There is a neutral start, various climbs that are attacked, and two sprint points. I'll walk you through how I look at and use the data produced on this ride.
A few weeks ago I did my last WNW for the year. For the total ride I averaged 242w and had a normalized power of 293 (Strava calls this Weighted Average Power). The big difference between those two numbers automatically alerts me that there must have been some large spikes in power to weight the normalized power so much higher than the average power. If it had been a straight time trial, my normalized and average power numbers would be almost identical. As I look at my Best Efforts Power Curve I affirm this to be the case as my curve contains some high numbers for this ride.
Jumping down to the curve I look for any places where the two curves are close or intersect. For this ride, I see that I set a power record (354w) for the 10 minute mark. While dragging your cursor across the curve, a black line appears. If you click the curve, the black line will fixate in that position and highlight the part of the route where you made this effort. This new 10 minute record came when I attacked the first climb and went on a 10 minute long breakaway. It was rolling terrain with a few climbs at the beginning and more flats and downhills towards the end. The group was better able to work together on the flats to catch me, whereas on the climbs there is little to no draft, so everyone must work equally as hard.
Taking a step back from this rides data for a minute, here is where the rubber meets the road. That new 10 minute power record gives me a reference point for the future. I know that during a ride, I am able to put out 354w for 10 minutes. But what does that get me? Well, the next time I attack a group, or hit a 10 minute climb, I know that is where I should settle in. I will pick a cadence that suits me for the climb and target 350 watts as I climb. If I feel good towards the end and my heart rate isn't through the roof, I'll push a little harder for the final few minutes and potentially set a new record. So your historical data becomes a pacing tool.
This is why knowing your power numbers is important. If you don't know what your 5 minute power is, then when you're doing a 5 minute effort, you won't know how and where to gauge your effort. Strava has made this particularly easy to do because of their Segments feature. On any given segment, you can filter the leader board to show only your times. Some segments I have done over fifty times and have lots of data to look at to see how I have improved. There are a few segments that I use to consistently to see how my fitness is progressing. How many watts am I able to average up the Jerome Jay climb? Am I improving in my 7 minute power duration? Checking your times up segments paired with your power numbers will tell you definitively what is going on. Some segments can be aided by wind or pack riding, thus your power number becomes the truth about how hard you were really going.
There are many power meter users out there that suggest doing independent power tests regularly is the best way to set your power curve data. While this may be the purest way to do it, because of the advent of Strava, I never get on a trainer and kill myself for 5, 10, 20 minutes. I do occasionally go out and do a test of sorts though. There is a climb in Roanoke, VA, that I try to hit every time I'm there. Its just about 20 minutes and a great place to test power. Typically I will ride easy for a bit to warm up before getting to the base of the climb, then I will hit it at 95% of what I can do (I rarely go 100% unless I'm racing). When I get home I'll look at the climb on Strava and see how I did.
Another tab that is helpful on Strava is the performance tab. This shows a more detailed view of what your speed, heart rate, and power was doing over a customizable duration. For any segments I hit hard with testing in mind, I often look at the performance to see if there were any spikes in the power, if it was steady over the duration of the segment, if it dropped slowly, etc. This might give further insight as to how you performed. For example, you may see a steady decline in power. That would indicate that you went out too hard. The goal would be to see the power as even and as "flat" on the graph as possible.
In conclusion, the two main things you can use a power meter for are monitoring progress, and gauging effort. With those two abilities, you can more easily identify your weaknesses with hard data, and adjust your training accordingly. The motivation a power meter brings also cannot be understated. I often find myself staring at my Garmin, watching the numbers as I climb. If I'm going easier than I am capable of, I can read it right on the screen, and it pushes me to go deeper. Again, power meters are exceptional tools. They can tell us all kinds of things about our fitness. This is the tip of the iceberg in all that you can do with one. So go out, collect initial data, know your power records, and using that as motivation, go set new ones.