Determining if one has a LSD

[Toby Erkson <Toby_Erkson@ccm2.hf.intel.com>]

Volks,
Through contact with a 914 mail list someone asked how one could tell if 
their car had a limited slip differential.  The replay was:  Jack up the 
rear of the car so both back tires are off the ground.  Make sure the 
e-brake is off.  Rotate one of the tires forward.  If the other tire 
rotates forward as well then you have a LSD (I believe the car did not have 
to be in gear).

Can anyone confirm this, is it a proper test?
     Toby Erkson
     air_cooled_nut@pobox.com
     '72 VW Squareback 1.6L bored and stroked to 2.0L
     '75 Porsche 914 1.8L for sale
     Portland, Oregon, USA