Hello, I recently created an apex class in the trigger. This apex class is to updating a field when a percent field is edited. I use more than 4 decimal places in this field. Sometimes, I can run the apex successfully, but in the meantime, I've encountered an error like the picture below : 
 
What should I do to manage a decimal field with more than 4 decimal places?

I ran simple query below and it gave me results:

select Id, name, userrole.name  from user

The child relationship name is called 'Users' on the User object so I was initially the query below but it kept erroring out:

select Id, name, users__r.name  from user

I thought every call to a parent must have '__r' appended but not in this case plus it doesn't even use the relationship name i.e. users. Can someone explain why the first query worked and the second one didn't...Many thanks...