Tracking fitness with the heart rate monitor

A while back I mentioned that I have this test where I run to Komazawa Park (3.8k), run one lap (2.15k) at continuing warm up pace, run the next lap accelerating to a heart rate of 149 (80% of HRmax) then run the third lap at as close to 149 as possible all the way. I've been doing this and accumulating the data, both in the raw pace for the third lap(red line) and as a kind of index (blue line). The index is something like "how many seconds of pace better than 5:00/km do I get for each heart beat greater than 130." It just allows some standardisation if I actually run a slightly different average heart rate, and it gives an increasing trend line instead of decreasing. Anway, both lines show that things have been going in the right direction of late. What is interesting is the big jump in September-- that is very largely weather related as our season changed from summer to autumn. But the improvements over the past couple of measures are unmistakable. Note that the pace for last Tuesday was 4:12/km -- doesn't mean I can run at that for a whole marathon, but gee, it is encouraging to be up in that ballpark again.