deltaTime()
A Number variable that tracks the number of milliseconds it took to draw the last frame.
deltaTime contains the amount of time it took draw() to execute during the previous frame. It's useful for simulating physics.
Examples

local x = 0
local speed = 0.05
function setup()
size(100, 100)
windowTitle("deltaTime example")
frameRate(30)
describe('A white circle moves from left to right on a gray background. It reappears on the left side when it reaches the right side.')
end
function draw()
background(200)
local deltaX = speed * deltaTime
x = x + deltaX
if x > 100 then
x = 0
end
circle(x, 50, 20)
end