[Gnuplot-info] (Version & System) Lines can't be drawn properly

[<ll...@ec...>]

Sorry, I forget to tell you my gnuplot version.
Version 4.0 patchlevel 0.
Ssytem: Linux 2.4.22-openmosix-2

I got some data identified by time. However, they are not sorted by time =
order.
When I used the command
"plot 'data.out' using 1:2 with l"
The curve wasn't drawn in the right way.
The data look like:
time    value
12:40    9
12:45    3
12:30    14
12:42    8
12:36    20

Thanks in advance.
Li