Showing trend data does not make sense if the number of days with measurements in the chosen time range is less than 5.
Please make sure you fixed the forearm during the measurements by placing it on a table or arm rest. In addition, make sure the outstretched hand can move freely. In rare cases it might be that a person’s tremor is extremely light, so that the sensors of the iPhone or iPod cannot measure them anymore.
Probably you did not record under comparable conditions. For example, in one case the forearm has been fixed, in the other case not, or the hand was outstretched in one measurement and relaxed in the next. Please make sure you always record using exactly the same position and fixation. The lighter the trembling is, the more important is that you are using the same recording condition.
Please refer to the pictures in the help section. Make sure the forearm is supported so that you only measure the hand tremor. The phone orientation is not important; however, you should always hold the iPhone the same way to make sure measurement are comparable.
If the trembling of a person’s hand is too heavy to hold the phone, you could use a workout/sports phone cover with a strap widely available in stores.