UKH

DIN settings on bindings are set by numbers. Does this assume that the spring tension on all bindings is the same?

Tables tell me that my DIN number is 6. My skis are ten years old so will the tension have weakened over time?

My skis were ok and disengaged properly it was just a question in my mind during setting. 

No, spring tension is always specific to that particular model. The end result is naturally that it takes tge same amount of force to release the boot from the binding. This all boils down to the binding designs, as they all seem to have slightly different leverage ratios, so naturally the springs need to cater that.
 

and Yes, the spring tension can decrease over time (especially If you run high settings and do not release the tension during off season). This is exactly the reason that shops will no longer install certain older bindings on the skis, even If they have Nothing wrong with them.

Thanks for the reply. Think I understand that. 

Also some ski shops do test DIN's if your a bit nervous about them.

Yes my ski shop did check what my DIN setting should be but he just referred to the online tables that I had referred to. 
On the occasions I’ve hired skis they have just looked at me and banged a boot out of the bindings deeming that to be ok. 

The DIN setting is usually read from a table from the binding manufacturer. The prime consideration is weight. It’s sometimes worth backing off the recommended setting for both age and skill level - so your skis release easier. Also, for no-fall skiing then it’s usual to ramp them up.

But don’t forget the correct forward load setting which pre-loads the compression force between the toe and the heel. This is just as important.

What Lankt meant was the shop testing your bindings to see if they release at the force corresponding to the setting on the scale

Indeed, but not many shops have that equipment (some do).

As for the table How to set the ”suggest” DIN. There are actually three variables. Boot Sole lenght, weight and lastly skill level. Often BSL and weight give the suggestion for Intermediate skier, beginners are then instructed to go -1 or something… and Advanced +1.5 or +2…. And experts already know What DIN they want.