Quite an Unusual one

[vargai]

To find the equivalent inertia of the 120kg gantry, you need to consider the effect of the ballscrew, so this formula is required (where L is the pitch of the screw):

Hi, I would like to apply this to my machine and wonder how it does come from ( see behind the formula)
That means this is not enough to count the reduced inertia on motor shaft with only the rotating parts?

120 kg*(0,01/2pi)e^2= 3,4 e-4 differs from your number.
Where I am wrong -Am I understanding everything well?
Thanks