Replying to How are skis measured?

I was out in Italy and France just after new year. The snow wasn't too great - rocks all over the place, and I had two core shots by the end of the third day so I rented some skis the rest of the week. The rentals were 190 Nordicas (definitely 190 - the skis' own graphics said so), but they were at least 10cm chorter than my 190 Volkl V-Pros when I stood them base to base. So, could anyone tell me how different brands measure their skis? Or are twintips measured differently to take into account the loss of running length due to the tail? Informed replies only please.