This is an Olympic version of FED 4b, also known as 4L (for 61 L/D lens).
With the last version of the black cover with horizontal and vertical stripes.
It's sad that FED decided to stamp 6-digit serials on the bottom plate of the back door, because those doors can be accidently changed easily.
FED-3, Fed-4 and Fed-5 doors are the same, stamping the serial on the door might have simplified production.
There are big, wide digits (more than 2mm high)
and small, narrow digits (less than 2mm high).
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