I keep track of several vehicles and the lifespan of the replacement
parts for them. The operators turn in a useage log at the end of each
day with the ending miles and operating hours, and our maintenance
records log the miles and hours at which parts are replaced.

Unfortunately, it is all too common to have the hours meter go out.
And the replacement doesn't necessarily begin at zero! This made
calculating the total hours lifespan of any part a convoluted mess of
several calculations thorugh all the hours changes.

I built a spreadsheet that contains a table of the parameter changes;
now I can enter the actual vehicle parameters at time of maintenance
and when the part was originally installed and it returns the actual
hours lifespan. I have to use one worksheet per vehicle, because I'm
trying to get by without macros - code confuses the others who might
use this! (I'm wavering on this - it would be much easier to have a
single user form than jump from sheet to sheet!)

This is good for a simple report on one major item that needed
replacement. But here's my dilemma: I need to integrate/implement
this into a comprehensive Excel-based report. The comprehensive
report worksheet lists all major items for all the vehicles. When I
generate an update to the report, I enter the new end-of-day
parameters for each vehicle and formulas subtract the item
installation parameters from the ending parameters to return the
item's current lifespan. A macro then inserts these current values
into a Word report.

Due to the convolutions in the engine hours, though, some of the
returned values are three or four times too much, and some are even
negative! Somehow I need to use my calculator to at generate a "fudge
factor", or at best be inserted directly into the formulas to get a
correct return value.

How would those of you with experience integrate/implement somehting
like this?

Ed