Crossed Axes

[Graham Gladman <swr97gjg@xxxxxxxxxxxxxxxxx>]

Hello,

I would like both my axes to go through the origin (0,0) in the middle of
the plot window in order to form a cross. The application is a
lag-correlation plot between two time series. So ideally the axis would be
centred on zero-lag, zero correlation. Diagramatically I have:
 _ _ _ _
|       |
|       |
|       |
|_ _ _ _|

Whereas, I would like:

    |
 _ _|_ _
    |
    |

I could achieve this by cancelling the default axes, and making my own
using ppl aline etc. This seems rather tedious and I feel there must be
some sort of qualifier that I am missing to change the axes to this
format. 

Thanks in advance for any help,

Graham Gladman