Thank you Vicky Wisheu for the feedback.  I like it!

"What about having students take photos of the different slides with a person or an object in them to give scale?  They could work out slopes and lengths with photos"

Vicky Wisheu

PS - Just a reminder that when you hit reply on your email the message just gets sent to me.  If you click on the Reply link inside of the email then the discussion forum opens and you can post a reply for everyone to see.  Thanks, Colin.