I have many rows of data with time stamps in the form of HH:MM:SS, i.e. 22:35:30. I need to lookup data in this table but the problem I am having is that the lookup values often vary slightly even though look the same, e.g. in actual number terms both 0.663460648148148 and 0.66346064814999 both display as 15:55:23 but the vlookup functions don't work because the ends of the numbers are different.

I plan to use the ROUND function to make the numbers the same. My question therefore is how many numbers should I round to in order to in order to keep the format always correctly in the HH:MM:SS format? This would have to work for any time of the day which is measured down to the second.

Cheers
-Rob

Ps - or any other method that might work but I need the times to be rounded to the nearest second. Thx.