Here is the formula in the screenshot figuring piston assembly inertia.

piston assembly inertia = Reciprocating Mass * CRANK RADIUS * W^2*(COS(Wt)+(crank radius/rod length)*COS(2*Wt))

W=angular frequency (crank rotations in 1 second times 6.28)

Wt=unknown

CRANK RADIUS=piston stroke/2

Please identify the Wt (omega t) symbol. thanks

Here's the screenshot: