The title is exaggerating a little, but I have tried to exactly measure how the tension in a racquet changes over time, including the effects of playing. I have therefore built a specially designed load cell that sits in the racquet (more below). I strung the racquet with a Kirschbaum Proline II 1.25 mm (polyester) string at 23 kg. I played with it after 5 days and then again after 12 days. The tension over the five weeks until it broke looks like this: Some things to note: The stringing took almost one hour, since I was measuring during the stringing as well (see this thread). The tension directly after stringing was therefore a little lower and the subsequent tension drop a little less than it would have been after a more normal 15-30 min stringing time. The racquet has been kept at around 18C during this period so the tension loss rate would have been a little higher in a warmer environment. An interesting fact is the the first match acted as a "fast-aging" of the strings, the tension dropped dramatically, but then stayed almost constant for a week. One of the main reasons for doing this test was to see how well my racquetTune app was able to monitor the tension drop. Since I am measuring two different things (two strings vs an overall figure) the absolute value would probably be different, but the trend would hopefully be the same. So taking the same data as the figure above and including the racquetTune results I got the figure below. In this case the x-axis is the time in log-scale, which makes the beginning more clear and it also makes it easier to compare the trends. I am very satisfied with the result and I think that racquetTune can be relied on to show the right trend of the racquet. Another interesting observation from the log diagram is that the drop (before the first match) is close to linear and can thus be described by a fairly simple exponential or logarithmic function. Set up The load was measured with specially designed load cell that sits in the racquet. It is made of high grade aluminum and has four strain gauges, two on each side, coupled as a bridge. This enabled me to detect a tension variation of 0.01 kg. It was calibrated in the racquet with another load cell/scale with a +- 20 g accuracy. This set up has been discussed in this thread /Sten ______________________________________ racquetTune, swingTool and netHeight, tennis apps for the iPhone.