clone - constraining horizontally

Hi, I want to sample part of an image and clone it at the same point on the horizontal axis but further along. Holding down shift doesn't seem to work for constraining any of the brushes along an axis. Is there a way to do this?

Thanks,
Mort

p.s. for Potatoshop 7

Hold CTRL+ALT and press the arrow keys.

hmmm, it doesn't work for me.
I hold ALT and sample the area I want to clone, but when I hold CTRL+ALT and press the arrow keys it duplicates the layer and nudges the contentst in the arrow direction simultaneously.

I want to constrain the brush horizontally.
Thanks for the reply. Perhaps I need to change my setting. Any ideas?

do you have aligned cliked on in the stamp tool options?.
i was able to do it perfectly fine.

Sorry - I think my explanation of what I'm trying to do was a bit fuzzy (the 'align' tick box controls the cloning sample point, which is something completely different from what I mean). Right. I'll think of a better way to explain

Okay, forget the clone tool for a sec. Say I'm using a brush and I want to draw a perfectly straight horizontal line. If I hold down SHIFT whilst painting and move my mouse to the right then the brush is only able to move horizontally. No vertical movement is allowed at all.

Now, with the clone tool I want to be able to sample an area of a picture, then release the mouse button, move the mouse further to the right (in a completely straight line - ie mouse-movment is constrained along the x axis only). Then when I'm at the desired point, I can start cloning the sampled point. This means I can start cloning at the same y co-ord as where I sampled....only the x co-ord has changed.

When I hold CTRL+ALT and press the arrow keys with the clone tool selected my mouse movement is not constrained at all. I can still move the mouse in all directions.

Sorry 'bout the poor explanation first time around. I hope this makes it clearer. Thanks for bearing with me :D

ps just incase this IS actually what you meant then sorry, no it's not working for me in PS7. WHen I press the keys I get the black/white double arrow cursor