How to calculate the negative growth rate?

How to calculate the negative growth rate?

The general formula for calculating the growth rate is to add an absolute value in order to eliminate the influence of negative numbers. For the first type, the profit growth rate = ABS [(- 50 + 100) / - 100] = 50%; for the second type, the profit growth rate = ABS [(50 + 100) / - 100] = 150%

Link ratio = (a-b) / B, if B is negative, or a is negative, how to calculate the link ratio?
What if a is 0 or B is 0?
If it was a loss last month, wouldn't it be negative?
I still can't understand. For example, we made a profit of 500 yuan in August and a loss of 1000 yuan (- 1000) in September. What is the month on month ratio in September? （-1000-500）/500？

Link ratio = (a-b) / B, if B is negative, or a is negative, how to calculate the link ratio in these two cases? If a is 0 or B is 0, what about these two cases? "Link ratio" and "fixed base ratio" are both methods used in statistics to analyze the data of real situation, and generally there will be no negative number