73 SV Echomap.

I am still learning my 73 SV. Question, how do you zoom in on SV while viewing in split screen with DV? I have noticed that the SV works much better in cleaner water, especially lakes where there is not any current. Any ideas on how to rectify this? Also, what brand makes the best, easiest mapping chips for this unit. Thanks for reading, regardless whether you can help or not.