An employee earns vacation at a rate of 1 of 9 tier levels (decimal fraction
of an hour for every hour worked), based on length of employment and part
time or full time status. We want to know when a tier level changes or is
about to change so we can update the payroll software.

Cell $c$2 is the current date
A3 answers the question: Is employee full time? We manually enter Y or N
B3 is date of hire
E3 calculates length of employment in years. ($c$2-d3)/365
F3 first looks at value in A3 and then compares E3 to Vlookup on sheet 2 and
returns the vacation factor (decimal fraction of an hour).
G3 looks at F3 and assigns a Tier level by using nested Ifs

Thanks