Stupid question of the week warning!!!
I have been taught this:
Fridge height say 9’ 6" + Unit (Scania) 4.3 = total height for indicator = 13’ 9" (still not sure how a unit can be 4’.3" above the trailer height, because it can’t)
Even if this is inches, why does the indictor have to increase by 4"
Anyone explain this please
Some trailers state their height only. In that case, you must add the height of the 5th wheel that’s holding up the trailer in order to get the total height.
This is because they don’t state their height from the ground, it’s from the rubbing plate to the roof. This is so that you can use different units of different heights and each driver will be able to calculate the overall height.
It’s an example of an error gate. If the driver has to calculate the height each time, it’s less likely that they will make a mistake, compared to using a trailer that states a total height for a given 5th wheel height.
Also, ‘ means feet and “ means inches, and 12 inches = 1 foot.
4.3 would mean metres to me
I assumed it was a typo since they also wrote 4’.3”
Who knows! But hopefully we’ve not found the next Litchfield Bridge Basher!!! 
Remember with 3 axle Scania units the ride height usually increases by some 3" when the lift axle is raised (some other makes raise slightly but nothing like the Scannys), and if you have a deep pin trailer, particularly one that slopes down towards the rear end, when you raise that axle the trailer leading roof edge might have gone up by 4"+…forget to pull the trailer air levelling lever out after tipping/loading and with the even steeper sloping back angle the front edge would be even higher.
Height stick preferable, but always carry a decent tape measure and learn your particular vehicle and all its idiosyncrasies.
Bridge bashing has reached stupid levels now, i am convinced this unit lifting issue has at least some influence on the numbers.
slowlane:
Some trailers state their height only. In that case, you must add the height of the 5th wheel that’s holding up the trailer in order to get the total height.This is because they don’t state their height from the ground, it’s from the rubbing plate to the roof. This is so that you can use different units of different heights and each driver will be able to calculate the overall height.
It’s an example of an error gate. If the driver has to calculate the height each time, it’s less likely that they will make a mistake, compared to using a trailer that states a total height for a given 5th wheel height.
Also, ‘ means feet and “ means inches, and 12 inches = 1 foot.
Perfect sense…thank you very much…all becomes clear now 
Just to make things more interesting, most fixed body trailers (boxes, curtain sides etc) have the height marked on them in meters. However, bridge heights in the UK are by law marked in imperial units. As councils replace old signs they have both units on them. But there are many old ones out there. So you have the added complication of converting from one set of units to another. As an antidote to this, I carry a small credit card sized reference card with conversions in 3 inch increments. If you can’t get one of them (can’t remember where mine came from) then there are conversion charts you can download and print out. I strongly recommend doing this, and carrying it with you.
Additionally, these heights on trailers are measured with a standard 5th wheel height of 1250mm. But some units - MAN’s spring to mind - that run at a higher setting. 1350mm in this case. That’s a whole 4 inch higher than a trailers stated height! But units with non standard heights usually have stickers advising you. Take a good look at your truck for them, including on the rear of the cab.
But the golden rule is, if you don’t know the height of your vehicle, don’t take it out on the road. And be extra careful if the height of your vehicle changes throughout the day.