Tips
Using the "@" in expressions...
You can use motion values from a different time with an expression like this:
[Object:xpos@25]
This will return the X-position of Object at frame 25.
[Object:xpos@NOW+25]
This will return the X-position of Object 25 frames ahead of the current time.
[Object:xpos@Slider:xpos]
This will return the X-position of Object at a "Slider"-controllable time. Since Sliders always use a 0-1 range, you can multiply the slider value with the desired range like the following for 250 frames:
[Object:xpos@Slider:xpos*250]
For better visualization of the result values, press the Debug button at the bottom of the expression list.
I didn't find that in the docs but in the amazing spider-scene that comes with messiah...
BTW. To enter the @-sign with international keyboards you can either copy/paste it from any text editor or use ALT + 064 (press ALT and enter the number on the numeric keypad)...
Expressions:
How to add channel code to expressions faster...