It's a seasonal thing I find, and very trend based.
For example one of my jewellery domains in December was OV with ex 112, now it's 10. Probably because the ladiez were looking for some bling.
Others are just bizarre. Like jtltd.co.uk which is OV with ex of 7. EH? And another thing why is there no OV result under 5 (I might be wrong). ????
