Hi:
You can do that by using the Vlookup fuction as follow:

Vlookup(Lookup Value,Table array, Colum Index (Return), Range Lookup)

Range Lookup MUST be equal to TRUE. This will return the closest value
matched.

Argy

"Scubaseth" wrote:

I have two data sets.
Each is two columns. Date/time and temp.
First data set has readings at intervals of 5- 15 minutes.
Second data set has reading every 30 minutes.

I would like to match, to the closest date and time, the second set to the
first.