Sagnac effect(question)

hi there

i've a question about Sagnac effect that can be found in ring laser gyroscope : https://imgur.com/a/UEaUkMh

in some papers they say that is linked to coriolois force,and due to invariance of light velocity during rotation of the device, is produced a phenomen: the red/blue shift which effects on the light beam that travels in the same direction of the rotation and for the wave that travels anti-clokwise (referred to the rotation)

-ok,rotation in the sagnac experiment is acted manually

-now in the case that the rotation isn't created manually,this rlg should be affected by the coriolois force of the earth?-and so from the phase shift measured by the detector what can be measured?- rotation of earth-how?

-this experiment can be associated to the rotation of the plane of rotation of the focault pendulum due to fictitious forces?-but in this case the F.F's change the "path" of light in the rlg (and so producing red/blue shift)?

thanks in advance