Algodoo

This is a spring where you can precisely control the length of it.
arrow up to make it longer and arrow down to make it shorter.
NOT PHUNLET SAFE!!!

How it works:
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it uses 2 custom variables, Scene.my.jamie and Scene.my.buster
scene.my.buster is it's target length and scene.my.jamie is the current length

here is the script
(e)=>{Scene.my.jamie < {scene.my.buster} ? {Scene.my.jamie = Scene.my.jamie + 0.0099999998} : {Scene.my.jamie > {scene.my.buster} ? {scene.my.jamie = scene.my.jamie - 0.0099999998} : {scene.my.jamie = scene.my.jamie}}}

for those of you who cant understand this, it is basically doing this.

IS JAMIE < Buster

yes: add 0.01 to jamie and ask again
no: IS JAMIE > BUSTER

yes: subtract 0.01 to jamie and go back to the first question
no: go back to the first question