check the new Ejs open source Vernier calipers java applet with objects and zero error logic.

September 08 2009
40. added object blue for internal jaws with proper constraints and push if touch and slider control http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1189
41. added green object for external jaws with slider control http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1189
42. redesigned the scaffolds for the zero error to reflect correctly the logic of reading with zero error
43. sync the pointers position to correctly reflect the zero error calculation
44. redesign the zero error slider to show 0.05mm instead of e=1 increment to be easier to understand
45. redesign the look and feel of the controls and the color scheme so it is easier to read white top scale on darkgrey top scale and light color bottom scale on black lines.
46. all new objects in Ejs 4.2 instead of the older objects drawing originally

it is most educational with inquiry possibilities now!  ;D
thanks prof hwang for your tips!
check it out. ;D :D