Eight letters that turn up everywhere. Pick one and it is drawn large beside a picture of the quantity it names — then move the single slider and watch that quantity, its unit and its formula answer back.
Symbol
θ
Greek lower-case theta
Quantity it names
Angle (plane angle)
SI unit
radian (rad)
Governing formula
s = r · θ
Live value
Angle in radians1.047 rad
Arc length1.047 m
Angle θ60°
Fixed: radius r = 1.00 m.
Try this: at θ = 57° the radian readout reads almost exactly 1.000.