Cell selection - starting from another cell other than the initial cell

Hi everyone, I have a cell selection question hopefully someone can answer

Let's say I'm at the bottom of a bunch of cells that have values with rows in between

I want to add up the cells (not a sum function - maybe there are other numbers between the values I want to add)

So in the total cell you hit "=" then keyboard up to the first number you want to sum, then you hit "+"

But here's the problem - the selection cell starts at the total cell and then you have to spend a bunch of time to keyboard up past the initial selection to the next value, hit "+", then start all the way over at the total cell and do it again, etc.

I'm convinced I remember someone using an arrow key combination such that instead of starting all the way back at the total cell after hitting "+", you'd instead start at the last value you added

(e.g. Total cell is C30, instead of starting there you start at cell C10, which is the cell you just selected after hitting "+")

Does this make sense? Am I hallucinating this ability or what?

Many thanks

I didn't know if there is one, so I checked Chip Pearson's helpful shortcut table, and I couldn't find what you're referring to.

...Well, if I was in your boat, I would create a helper column adjacent to the data for "add this row yes/no" and then push the helper column and the summation column into a SUMPRODUCT or SUMIF, and not have to change the formula after that, only the helper column.