Sleep Cycle needs one, sometimes two, nights to calibrate to your accelerometer. Usually the calibration is not needed but on some (very few) devices the accelerometer is too sensitive and can detect movement when there was none during the first one or two nights. If you place your iPhone/iPod in bed, according to the instructions, then this is not a problem.
When calibrated, Sleep Cycle is extremely sensitive to movement. It can detect the slightest vibrations. For example, you walking past the iPhone/iPad or a car/truck passing by on the street outside.
When you place your iPhone/iPad on a flat surface then Sleep Cycle detects very little movement. It then assumes that the users movements are very difficult to detect and goes into a mode where every movement is treated very seriously (and creates a big spike in the graph).
If you still feel Sleep Cycle creates inaccurate graphs, please do not hesitate to contact us. We’ll analyze your data and check if you have discovered an issue with the Sleep Cycle movement-detecting code.← Sleep Cycle detected movement and created a graph when I placed it on a table during the night. Why?