If a laser interferometer, positioned paralel to ground, measure rotation speed, what measure when vertical?

Question

As you know, a ring laser can measure rotation speed when it rotates around own axis (perpendicular to own's plane).
This kind of device can detect rotation speed of the Earth. But, for measure this speed, this device is placed paralel to the ground, (please see this pages:
http://www.ringlaser.org.nz/content/about_us.php
http://www.ringlaser.org.nz/content/gross_ring_facility.php)
Why the ring laser is paralel to the ground, when is suppose to be perpendicular to Earth's rotation axis when measure rotation of the Earth? What should measure then a ring laser when is positioned perpendicular to Earth's rotation axis?

http://www.ringlaser.org.nz/content/gross_ring.php

Answer 1

Remember, rotation is a vector. The device measures the component of rotation about it *own* axis, directly. The component of rotation of the loop about its own axis due to earth's rotation = once per day times cos(theta), where theta is the angle between the two axes. The loop being perpendicular to the earth axis makes both axes in the same direction, resulting in the the strongest signal. If you lay it flat on the ground, theta = latitude.

Answer 2

when u place parallel to the ground it wouldnt measure the rotation speed. when u place the laser perpendicular the it will measure the rotational speed when it is parallel it will travell like light

click on the links below
http://en.wikipedia.org/wiki/Image:Sagnac_interferometer.png
http://en.wikipedia.org/wiki/Ring_laser
http://en.wikipedia.org/wiki/Sagnac_effect

Answer 3

maybe axial speed?