How to hide a number value in a column so people can't see it, but the autosum button still counts it at the bottom

For example at work I have to do a certain number of cases with different number documents by the end of the day and it's all logged in a specific column. I basically have to do at minimum 600 images worth of documents logged, and its tracted on the sheet.

How do I add an extra number to the columns, (like for example if I put in a "5" I want to say include an addition "10" to make that column add up to 15, but still only show 5), and that way the autosum feature at the bottom will count 15 and not 5 (in addition to all the other documents I do adding up to the 600 minimum)

I know some people say to simply change the font color of the number to "white" so it blends in with the background, but that doesn't really work for me because the first number still needs to be shown. So how do you "hide" a second number in the column so it gets counted by autosum?