cool thing about construct is,
often times, you can translate your thoughts pretty directly to events:
since there is no On Control Released condition (there might be one in the Custom Controls plugin, I don't remember), I'll be using 'left mouse button' instead of "fire" in this example:
we are going to assume that 'power' starts at 175 when you start holding the button:
<img src="http://dl.getdropbox.com/u/1013446/s/powerpro/1.PNG">
I want, while the "Fire" control is held down and 'Power' is below 700, to increase the Power in increments of 175 every 200 milliseconds.
<img src="http://dl.getdropbox.com/u/1013446/s/powerpro/2.PNG">
Once the "Fire" control is released, the projectile is shot at the speed of 'Power' pixels per second.
<img src="http://dl.getdropbox.com/u/1013446/s/powerpro/3.PNG">
altogether:
<img src="http://dl.getdropbox.com/u/1013446/s/powerpro/all.PNG">