After driving a B Double all last week I could not help but notice the amount of cars that had there cruise control set on 100kph when the car was only doing 95,96.They should have realized that when cars and trucks(speed limited) were passing them that there speedo was incorrect.Please put a navman in your car and check your speed as 90% of the time you will find it incorrect.For a B Double to pass it take a long time as it can only do 100 (give or take 2klm depending on tyre wear and speed limit setting). You may wounder why that big truck behind me wants to pass when I am doing 95klm. The main reason is I am only aloud to driver 12 hrs a day and carting livestock they do not like standing in the truck for 12 hrs in 40 deg heat when I am up the front with my cooler going looking around and can not go anywhere because of my work diary(log book). Loading time is included as driving time in the log book and so that took many hours away from actually driving time.This is why 5klm by 10 hrs is 50 klms a full 1/2 hr drive extra and in my case that make the difference of legal or not because for the animals sake I could not let them stand there for 12 hrs just for an illegal short drive.There are many many trucks driving to there legal limit.If we do not get caught behind slow cars and caravans we can make it legal so please check your speedo and this also makes it safer on the roads.The idiot of the week was a car followed me for about 5klms with many a many bits of strait road but finally pasted on a bend putting myself and the car coming in to the dirt(luck I was watching)Thank you for taking the time to read this.