The explode button has been disabled by the developers shortly for bugfix reasons. Expect it to be readded soon
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The accuracy slider is, well, it's hard to explain. So imagine you've got a planet orbiting a star every 3 days, and the simulation measures 6 positions in the orbit. If you increased the accuracy by 100%, it would measure 12 points, if you decreased it by 50%, it would measure three points, and so on and so forth.