Differently for standard oscilloscopes, in HScope you can select the acquisition rate of the oscilloscope. Selecting the rate means to set how many points/second (or Samples/s) you want to use to scan the input signal. After selecting the rate you can choose the time/division.
This value is also related to the maximum frequency you suppose to find for your signal. Assuming your signal is a Sine like shape you may practically need at least 10 points inside one period.
So with a rate of 100 KS/s (Kilo Samples / second) you can see well waves till 10KHz. If these waves have faster variations then you need to increase the rate level.
Square signals has infinite bandwidth, so they may requires high sampling rates to see well the edges.
Roll mode rates are slow rates indicated in blue color in the rate list selector. At these rates the signal update in real time on the main screen going from left to right.
Currently is is not possible to use Trigger functions with a Roll Mode rate.
If the signal is not stable on the screen sometimes it is because its frequency is very low respect the Sampling Rate, so during one (very fast) scan the Scope cannot see and recognize one complete waveform. In this case just try to lower the Sampling Rate.
Roll Mode works for low sampling rates and allow to see the signal taking shape in real-time on the screen in continous and unlimited refreshes from left to right. It is still possible to use rulers and take measures while the signal update in real-time.