Time to get creative! I suggest you rebuild the whole tracking system
and impress your boss. Whose idea was it to have an entire year across
the top of a spreadsheet? Why start with January on the extreme left
of the spreadsheet, when you have to scroll WAY to the right to find
December, and probably no longer care about January anyway?

As an idea, and I admit a lot of this depends on the type of rental
equipment you have, why not devote a tab of the spreadsheet to each
piece of gear? That way you can develop and assign usage codes, and
vertically (and almost limitlessly, since you'd have 65,000 entries per
machine within the spreadsheet) track each welder / crane / lift
truck's time out in the field, transit time from location to location
(I've been to TX, and I know it's a wiiiide place!), days scheduled to
be out of service for routine maintenance and thereby not available to
customers, days out of service due to repair, the per day or per hour
price quoted to the customer, or hours in service, or what have you.
Then later on, you can tell Boss Man, hey, this company rented this
machine for X days last year, why don't we leave it at the El Paso
warehouse so it's easier for them to retrieve, or hey, this machine
spent so much in repairs last year we should consider replacing it, or
this machine spent so many days idle we should sell it and cut our
losses.

My point is, make the software work for YOU, instead of trying to beat
your head against the software.