I have some output from a database listing chargeout rates for various
contractors. As these are updated yearly, there are various values for each
contractor, and each change has the date it was instigated.

I need to be able to reference this data to find whatever the chargeout rate
was on a given date. The thing is, a normal lookup needs exact values, and I
cannot work out how to get it to return the value on a given date.

Any suggestions?