Sonoline B Fetal Doppler

Has anyone ever used the Sonoline B fetal Doppler? I got mine and im somewhat understanding how to use it but I'm sooo confused about the modes 1-3. What are the uses for each mode? The instructions are horribly useless .. lol

(I also made a post in general pregnancy)

Here is a picture of it. The number next to the heart is the mode it's on and there are 3 modes. You change the mode with the furthest left button. I tried Google but haven't been able to find anything about the modes. Heeeelppppp

Fyi, I am 18+6 and was able to find a HB just don't understand the modes and their uses..