[motr]Thermometer[/motr]
The Applet of Thermometer is to understand the concept of minus quantities.
To understand easily, it asked the studends to compare the degrees between two days.
And it instructs them one of the concepts of minus quantites as the defference quantites between two things.
Applet of Thermometer
http://www.ies.co.jp/math/java/geo/therm/therm.html