if his boss is willing to write that letter i would get it done and hold onto it. you never know what you might need later and the person who is going to write it now may not be with the company or willing later. Once you have the letter you have it. you wont have to persue it and perhaps not be able to get it. Finz is dead on about what needs to be shown, but the supervisory part may be part of that or may not be, at least you would have what you need. Ive gotten important letters from people who i thought would be around for quite a while but moved on and it paid off for me.