Google Sheets Formula Sometimes does not work with Merged Cells - google-sheets

Question

So I have created an invoice spreadsheet in Google Sheets and have used merged cells extensively in order to create a cleaner look for the invoice.
Here is the problem that I am having: sometimes, my simple subtraction formula does not give me a correct result. The formula is supposed to subtract the Unsold balance (cell V27) from the Beginning Balance (cell R27).
Again, there is nothing wrong with the formula itself, as it works correctly 99% of the time, but every now and then, it just gives me an answer matching the Beginning Balance.
Also here is a link to a copy of the spreadsheet for anyone willing to take a look. https://docs.google.com/spreadsheets/d/1bf_QE-u36mo4AKyqg7Dk11gwoR0p5g0qveIazR83Xbk/edit?usp=sharing
Has anyone else ever had this situation happen to them? What could possibly be causing it, and more importantly, how can it be fixed to be more reliable?

Answer 1

Those of us who work professionally developing Sheets solutions have a few basic rules that we follow and encourage others not to break. Among them is "Never merge cells anywhere that calculations or comparisons will be (or ever might be) performed or assessed."
While what you're seeing might seem to be a glitch, I wouldn't call it that. Merged cells don't really get rid of the cells you don't see. For instance, your cell R27 doesn't "get rid of" cells S27, T27 and U27. It just holds them in memory, presumably empty. But remember that, inside Sheets' "memory," it doesn't "see" a grid. It's just 1's and 0's. When a grid is new and no cells are merged, Sheets "finds" each cell (using the best analogy I can give) counting over and down by 1's and 0's that are very small and tightly packed. Hold that thought...
Also note that many people are surprised when they have multiple complex calculations going on and get a returned answer that is off from what they expect in a cell further down the calculation chain. This is because Sheets uses floating decimal points. For instance, "one divided by three" is about 0.333. But in reality, that extends very far out: 0.33333333333333333333. But that can't go on forever or Sheets wouldn't be able to run. So at some point it gets truncated. Eventually, those extra decimal-extras will start to add up and bump numbers up (or down) by small degrees. All of this is handled by the same 1's and 0's that run everything else.
Back to merged cells. Finding and accurately "reading" merged cells gets less accurate the more of them you merge, because the process is relative to other cell locations in memory. After a while, the "floating decimal point" nature of Sheets starts to lose track, especially (I've observed) if you've got merged cells using the same sort of relative formula reference that you're using (e.g., a lot of your stacked merged cells are referencing yet another merged cell: BB2. So (again by analogy), Sheets is trying to "guess where it is by using clues." Perhaps it found something correctly in merged cells Z-AA-AB-AC23 that referenced merged cells BB2-BB3-BC2-BC3; but that time, you asked it to add merged cells R-S-T-U23 and V-W-X-Y23 and subtract merged cells V-W-X-Y24 ... where in the following set of merged cells, Z-AA-AB-AC24, you still asked for the BB2-BB3-BC2-BC3 reference but not the V-W-X-Y24 subtraction. And so on...
To add to this, you've got row heights changed all over the place. Some are set to specific heights, while others are fit to data.
You get the picture.
If Sheets is trying to find things by moving over and down from cell A1, but there is no regularity, sometimes, it just throws it's hands up and says, "Where the h-double-hockey-sticks am I anymore?" When you then reload the sheet or delete and replace the formula, it starts out at A1 again and plays Chutes and Ladders on the broken board and might shift one "floating" teeny-weeny 1 or 0 a different way from last time... and find what you wanted it to find again.
You also-also wind up with a sheet that is 56 columns across, when you probably only needed it to be 12 or 15. Likewise, you've extended the number of rows beyond what it needed to be. So you're slowing down your processing by a lot.
THE SHORT VERSION:
As nice as merged cells might look, they are a computing nightmare. I've been working with spreadsheets since they were invented, and I've literally never had a need for merged cells (though I've occasionally used them in areas that are purely aesthetic).
THE SOLUTIONS:
1.) Remake the sheet without merged cells.
-or-
2.) Try encompassing all of the merged-but-hidden cells in your calculations. This at least gives Sheets a wider net to cast. For instance, in your example above, you reference this formula:
=IF($BB$2<>"Rental","",R27-V27)
Try (where possible) to include the whole range you merged:
=IF($BB$2<>"Rental", "", SUM(R27:U27) - SUM(V27:Y27) )
Technically, you could also include all cells in the BB2-BB3-BC2-BC3 merge:
=IF(AND($BB$2<>"Rental", $BB$3<>"Rental", $BC$2<>"Rental", $BC$3<>"Rental"), "", SUM(R27:U27) - SUM(V27:Y27) )
However, try the shorter route with just the SUMmed merged ranges and see if it holds up. If so, stick with that. If not, go with referencing every cell in ranges you merged.
You've clearly put a lot of work into setting up this sheet. So I'm sure this isn't the easy answer you were hoping to hear. But I hope it does give you some direction for next steps.

Answer 2

For me, the simplest solution is to lock-reference the uppermost cell of the merged cells.
Instead of referencing in the top formula as B2, reference as $B$2. This way, your formulas in other cells will reference the same value as required.
USE LOCK-REFERENCING:
$B$2