In column C, type formula:
=A1+B1/24/60/60
and then format it as:
hh:mm:ss.000
--
Best regards,
---
Yongjun CHEN
www.XLDataSoft.com

=================================
"Callum" wrote in message
...
In column A I have the time in hh:mm:ss (13:36:05) format, in column B I
have
the millisecond value (0.256). I have 3000 rows of data in this format
and I
want to combine the columns into one column of format hh:mm:ss.000
(13:36:05.256)

how do I do this? I've tried "concatenate" but I think this only works
with
text (does it?)

Can anyone help me?

Thanks in advance, this is proving a real head-ache for me.

Callum.