FED 5 light meter problem

I just got a FED 5 in the mail today and the light meter is off. While the needle moves, it only maxes out at a 4 when pointed towards the sun (lens was covered to protect shutter curtains). Is it possible to adjust the meter and if so, how?

Selenium cells do die with age (and especially exposure). Though FED cells often seem somehow to be fairly resistant to that.
Not knowing what "4" means right now, if the values are very off (more than 3 stops or so), it probably can't be adusted and the selenium cell must be replaced.

BTW: While curtains being burned by the Sun can happen, it takes much more than a few seconds....

The meter has numbers on it from 1 (lowest) to 11 (highest), so it is pretty off....