grow an arrow across the screen...how?

You may be able to use a Magic Move transition.

First, copy and paste the slide. Next, on Slide 2, extend the line to the length you want. Then go back to Slide 1 and apply a Magic Move transition. When you run the presentation, it will look like you have only one slide with a line that grows. Note that you can "chain" multiple Magic Move slides so that the line can grow and stop, then grow and stop.

Magic Move cannot transform most shapes who's anchor points or 'shape' changes, except in the case of a uniform change in scale. Lines that have one anchor-point shift relative to the other will not MM. Interestingly you can change the colour and it will crossfade nicely.

Magic Move can stretch a rectangle though. So if you move the arrowhead as a separate object from the line, you can do it. You can even non-uniformly scale the arrow head so it goes from 2 times line width to same as line width and MM will smoothly scale it down across the move.

The are many ways to do this with build actions also. Main thing is to separate arrow head from the line to give better control over scaling. Previous threads have covered this if you care to search, here's one:

How to animate height OR width dimension (but not both!)?

wideEyedPupil wrote:
Magic Move cannot transform most shapes who's anchor points or 'shape' changes, except in the case of a uniform change in scale. Lines that have one anchor-point shift relative to the other will not MM.

On my system I can get a line to MM. I put an arrowhead line on Slide one, duplicate the slide, then stretch the arrow end of the line across the second slide. The MM works just fine.

Apologies Tulse, it doesn't MM on my KN09. Are you using the thin arrow lines (top of menu) or thick arrow lines? (Or both?)

Just double checked and set to 3 sec transition so I can see it, it's a dissolve for both kinds of arrows. This is odd.

wideEyedPupil wrote:
Just double checked and set to 3 sec transition so I can see it, it's a dissolve for both kinds of arrows. This is odd.

That is strange, as my relatively old PowerPC PowerMac is definitely moving and not dissolving. Perhaps it's a video card issue?

My GPU: GeForce FX 5200 64Mb. Guess it's time for a bug report. Snow Leopard (Intel only) will probably change everything too.