If you look at the weight trend graph for in the app, it shows the last 7 readings. Those readings are evenly spaced across the X axis instead of being over the actual time between readings. If I weighed myself on a regular basis (say daily/weekly/etc) this would be fine, but I do this irregularly.
E.g. If I weigh myself on July 1, 2, 4, 8, 16, August 1, and then September 2, the readings would be evenly spaced across the graph and not spaced out based on the actual time between measurements.