How can they claim 16h of work - I own an Asus m16 with the same CPU and a 90Wh battery and after some tweaking my Ubuntu drains 9.xWh without touching anything

How can they claim 16h of work - I own an Asus m16 with the same CPU and a 90Wh battery and after some tweaking my Ubuntu drains 9.xWh without touching anything ... With Firefox open it already consumes 12wH - so I guess I can be happy if I can get 6h of work done with one load and this laptop here can't do much better...