Drop down without source

[TheSubject]

Hi,

I'm creating a cash-up sheet for a bar, and I'm keen for various phone-usability related elements.

I've found excel on phones handles drop downs far more smoothly than raising up the keyboard after double tapping a cell, so zoomed out so you can see other cells but not so zoomed out you can easily miss the cell.
I also can't expect me and my supervisors to all have the same type of phone or excel app, and own skills with devices and excel.

So I want a drop down for each denomination of notes, ie,[ 20s x ][<dropdown>] where the [ ] visually represent the cells and the <dropdown> then displays a list of options, ideally as "1 = £20", "2 = £40", (I want to make this really idiot proof!).

Obviously I can guess - we will never take over 5000 in just 20s, etc, and worse case scenario, in the comments they can right "half the 10s are 20s your stupid sheet doesn't work!" or whatever, but really I want an endless list, that displays the "idiot proof" formating, but for cells referencing it, counts as the value.

I've briefly experimented with putting basic formulas into the source bar but haven't had much luck understanding what works or not. That would normally be fine, I love poking around excel, experimenting, but I also am keen to make a great impression very quickly in a new unexpected promotion! So, any help (ie, the direct formula) would be great, but if that just sounds a bit lazy on my behalf, then at least please answer:

Is this possible? without visual - which I am a novice in and whilst I hope one day I can start learn, today isn't that day!


Thanks for reading, and for any help in advance!!!