Hi, unhappy, You may think that this is off topic but it is worth bearing in mind in the general field of computing, particularly performance reporting.

The theoretical range for percentages is from -infinity to +infinity. If you think about it, those are the results of division by zero That is why computers scream blue murder when you ask them to divide by zero, as you have asked them to calculate infinity.

You need to keep an eye on this when you are doing marketing, sales, product reporting, etc. over time. You could well have a valid divide by zero if there were no values in the previous period. It could also be an indication of some sort of data collection error or corruption. To use blank, 0, or - is not correct, and could be misleading.

I prefer "dead eight", inf., or "not applicable (N/A)

In any case you need to intercept the standard divide by zero error condition message.