Every standard Income Statement in Business Central contains both revenue and expense accounts. A typical comparison report includes a column for the relative change in percent, where A is the current period, B is the prior period and C is the absolute variance (A-B).

Business Central provides the "Show Opposite Sign" flag at row level. When correctly configured, this ensures that absolute values are displayed with the economically correct sign for both revenue and expense rows.

However, the percentage change column still produces wrong results for expense rows, because the formula engine does not respect the "Show Opposite Sign" setting when calculating formula columns. Currently, percentage change can only be implemented using the native BC formula C%B, which supports no ABS() function or conditional logic. There is no setup combination that produces correct results for both revenue and expense rows simultaneously.

The fix would be straightforward: introducing an ABS() function into the column formula language. This would allow the formula (B-A)/ABS(B) to be used instead of C%B, which produces the correct percentage change for both revenue and expense rows when "Show Opposite Sign" is properly configured. This is a fundamental reporting requirement that affects every Business Central user building a standard P&L with period-over-period comparison.