You can use what ever values you like so long as you set all of them using the same scale.
If you use 1, 2, 3 then the one with a 2 will be twice as important as the 1 and the 3 is three times as important, likewise 10, 20, 30.
But if you only set one of them and use a 10 then the others will still be at their default value of 1 and you will set that one to be 10 times as important as the others.
-Jeff