Q:

Permission Set settings to edit certain fields

I'm trying to use Permission Set to grant some users the ability to edit an object, with the caveat that there's 1 field that is not editable to them.  I've tried setting the Object Level Security for that Permission to include Edit, and for the Field Level Security I uncheck Edit for that particular field.  However, when I log in as a user with that Permission Set I can still edit the field without any errors.  I also tried to exclude Edit in the Object Level Security and manually check Edit for all other fields in Field Level Security, but it ends up not showing the Edit button at all; so now I'm stumped...
I'd really appreciate any pointer from you guys, thanks in advance! 

A:

https://success.salesforce.com/answers?id=90630000000gkeYAAQ
I recommend reading the above answers as the discussion clarifies what wins the race .Permission sets are meant for extending the accessibility not restricting the accessibility. 
In your case you are expecting restriction through the permission sets by not checking edit for the particular field ,which is not possible through permission set if the profile already has the access to the edit the fields . 
Rule of Thumb
"Among Profile & Permission sets whichever provides greater visibility wins the race."  Permission sets extend users' functional access and not meant for restriction 

