Temperature & Humidity Data Logger / Recorder

Hi
Just wondering has anyone any experience of using these devices, they look quite good.
It's an area of my growing process which I would like to control a little better. I feel if I could monitor the complete environment more closely I could improve on my yield etc. Because I can only access my grow area during the dark hours I can only monitor my temps etc for a few minutes at a time.


http://cgi.ebay.com/USB-Temperature-Humidity-Data-logger-Datalogger-Monitor-/270686250813?pt=LH_DefaultDomain_2&hash=item3f0628673d

Is there any other cheaper methods of recording these variables on a 24 hour basics?

Wondering if you ever used this. I'm picking one up next week from a friend who sells these and other instruments. I was thinking the same thing as far as giving me a good overall outlook at what my room is doing over a 24 hour cycle. Wondering if the data helped you tweek your room?

Picked up one of these yesterday, http://www.testequipmentdepot.com/reed/rh-data-loggers/st-171.htm

I've set it to take a temp/humidity readings every minute. This allows me to track up to eleven days by the minute whats going on min my veg room. I'll let you know if this helps me control my room any better.

here's a tech/software demo on YouTube http://www.youtube.com/watch?v=IesbTpyukF4&feature=related

Here's a little over 24 hour snapshot of what my veg room is doing minute by minute. Interesting to see the humidity climb and then a big bump in R/H when the lights kick on and the plants start to absorb light.