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Hit d and click to create and select a new object with a single point, and add more points to a selected object.

Hit v and click to set the velocity of a selected object.

Hit n to deselect.

Hit u to remove the most recently added point from the selected object.

Hit s and click near an object to select it.

Hit k to remove the selected object.

Hit c to add a clock to the most recently added point of the selected object.

Hit z go to the frame with x velocity 0 and y velocity 0.

Hit m to match the selected object's velocity.

You can save what you've made by converting it [to JSON], and you can load something already made by loading it [from JSON].

You have to be in the frame with x and y velocity 0 to edit.

Speeds are unitless and go from 0 (motionless) to 1 (speed of light).

Times are measured in seconds.

Clocks display a subsecond hand that goes around once per second and a second hand that goes around every 12 seconds.

Clocks are set so that in the frame with x and y velocity 0, they display 0 at time 0.

Distances are measured in seconds, ie, how far light travels in one second. There are 60 pixels per second.

The start time and end time are measured in the frame with x and y velocity 0. So, if you have start time as 0 and end time as 5 and are in the frame with x velocity 0.99 and y velocity 0, the simulation will take very long to reach the end time.

Points and velocities are snapped to a grid whose size you can specify below.

After changing something in a text box, make sure you press the corresponding button or changes will not take effect.