Things to remember - Google Sheets - how to show the last number in a column

I have a Google Sheets file that I put all the water information for our farm into. It's fairly comprehensive with formulas etc to let me know the following once I measure the water level from the top of the tanks:

• volume of water remaining
• amount used since the last recording date
• average usage since last recording date
• amount of rain we can have until the main collection tank overflows (so I know when to pump it up to the feeder tanks)

I would like a summary of the actual levels in each tank in a nice little chart that I can import into our personal intranet site hosted with Google Sites (this part is ridiculously easy), but I don't want to have to change the site information overtime I think about it. 

I found this:

=FILTER( A10:A100 , ROW(A10:A100) =MAX( FILTER( ArrayFormula(ROW(A10:A100)) , NOT(ISBLANK(A10:A100)))))

Now if you put that into a cell, alter the ranges to suit, it will give you the last number in the column (and maybe row, but I haven't tested that). It works very well - not only for numbers but for the dates as well. The little summary chart now shows:

• The Date of last reading
• amount of water remaining in each tank
• amount of rain we can store until the collection tank overflows

And with Google Sheets adding in some decent conditional formatting I have it all colour coded and it looks a bit like this:

Not bad eh? The bit that tells me the overflow is elsewhere on the page. And yes, we're in pretty decent shape given that it's the start of Autumn and we should get rain soon!

Google Sheets - inserting a static variable

Ever had a spreadsheet with set variables and wanted to use them in a formula but not have to type them over and over - just use the drag down feature and have it work? For example, if I had a formula where I wanted A3 to be present as part of it, and when I try to apply that formula to multiple cells the A3 becomes A4, A5, A6 etc? That's very annoying and up until now I've gone through and manually corrected it.

Not any more! By putting a $ sign in front of the column ID and the row ID e.g. $A$3 - it won't change! It stays the same! OMGWTFBBQ!

How long have I looked for this - I found the answer here: http://www.gcflearnfree.org/googlespreadsheets/14.3 - read up for more info! Yay!