Retrieve Offset value using search in a variable external reference

Hello.
I am an Excel novice, so if what I've done so far can be improved, like NOT using volatile INDIRECT formulas, I'm very open to suggestions.
I am attempting to create a water bill Invoice generator worksheet with values retrieved from tenant (Unit) worksheets, each of which is identical in layout. Current water meter values will be manually updated in the tenant worksheet. The Invoice worksheet has drop-downs to select the appropriate unit, the meter start date, the meter end date. A lookup is performed based on the select unit sheet and meter end date to retrieve the current meter reading value (see the Invoice worksheet) This is working fine. It's when I try to perform an offset to retrieve the previous meter read in the column to the left of the current meter value that I'm running into problems (see the UNIT worksheet)

INVOICE Worksheet


UNIT Worksheet

Never mind, all. I was able to answer my own question.