Displaying data in a chart sorted by timestamps

Hi, i currently have a problem with a chart presentation.

I have the following data-setup:

A collection of temperature readings done at 10 second intertvalls:

B1 C1
25.10.2011 03:11:33 137,1
25.10.2011 03:11:43 137,2


A collection of temperature readings done when an external signal is provided:


B1 C1
25.10.2011 03:11:30 138,1
25.10.2011 03:12:53 139,2

I tried making a line chart with a separate line for the different readings but the problem is i cant get the second collection to only present the values at the specified times.

if i choose a category axel with times i only want the temperature readings presented when theres a corresponding time for the axes:

like this:

100 o
------
80 x x x
-----
70 o
---- x o

11:00 | 11:01 | 11:02 | 11:03 |

At the moment the values are presented disregarding the time axis

so if i have a continous readout of values at a specified interval

i can present them as one line in the line chart.

but the second noncontinous readout will not present the values at the actual time when they were collected. they will instead start at the same point as the first data readout.

Hopefully someone can get the concept of my ramblings, since im trying to do this in a swedish version of excel some of my translations from swedish to english may be off target... :D

Best regards

Mikael