In the winters, I run on an indoor track, and use a footpod to calculate my distances with my GPS watch. The facility has three lanes, inside #1 is 181.6 meters, middle lane #2 is 187.2 and outside #3 lane is 194.3 meters long. The track is more less rectangular shaped as opposed to a circle, but with circular corners. I try to calibrate my foot pod with roughly 5 laps to 1 KM, so I run where a 4th lane would be, if it existed. My simple calculations have the imaginary 4th lane at about 203 meters. I arrived at this figure by taking the percentage increase of each lane - lane #2 is 103.0837% of #1 and #3 is 103.7927% of #2. The difference in % increase between #2 and #3 is .7090%. So I arrived at 203.0469 meters for #4 by multiplying #3 distance of 194.3 * (103.7927% + 0.7090%) - in effect adding the percentage difference from #2 to #3 to #3's percentage increase compared to #2. To clarify more I've attached a screengrab of my calc's in excel. (Column C is difference in meters from #1 to #2 and #2 to #3, and was not used in calc's for #4, column D is each lane divided by the lane inside it, formatted to percentage) Did I use to correct formula to arrive at the distance of a 4th lane?