Timelapse photography using CHDK

I thought it could be fun to do some time-lapse photography now that I have a programmable camera. So I have quickly whipped up a small time-lapse script that works on my Ixus 750:

@title Timelapse
@param a Number of steps 
@default a 30
@param b Period (seconds)
@default b 60

rem Sanity check.
if a<1 then let a=1
if b<5 then let b=5
let b=b*1000

rem Take the pictures!
for s=1 to a+1
    rem Take a single picture.
    print "Shoot", s, "of", a
    press "shoot_half"
    sleep 2500
    press "shoot_full"
    release "shoot_full"
    release "shoot_half"
    print "shot done"

    rem Sleep until its time to take the next picture.
    sleep b
next s

At the standard setting it takes thirty pictures in roughly 30 minutes.