Charting Conventions with Primary & Secondary Axis

Good Evening

I have attached a simple example of a chart with a primary and secondary vertical axis. The primary reflects $values from negative to positive. The secondary reflects percentages beginning at 0. My questions are:

1. Are there any conventions that dictate how to hand this situation?

2. Is it possible for the primary to begin at ($6000) and the secondary to reference from the 0 primary value?

Thank you for taking the time to read and answer this question.

Al