Macro - Sum Up, Compare, Display

I have a spreadsheet with three sheets („Data”, „20” and „30”). On the Data sheet I have only two rows, and I do not work on this sheet. I work with the sheets 20 and 30. On the sheet 20 I need to sum up the amount of column H. But my problem is that the count of this column (the rows or cells) allways change. Sometimes there are 554 the next day 663 and so on. So I need the macro to sum up the amount of column H two cells under the last cell. I need exactly the same in the sheet 30, but the only difference is that in the sheet 30 the amounts are in the G column (not in H). Finally I need to compare the two summed up amounts (sheet 20 and 30) and they must be equal. So what I would need as macro is that when I run it, it sums up the amounts in both sheets and then in the Data sheet (in the 5th row, cell A) displays the summed up amount and (in cell B) displays OK if the two summed up amounts are equal, or just dislpays ERROR if the summed up amounts are not equal.