Olympus eyepiece markings?

[Leitzcycler]

What does mean in Olympus eyepiece the following?

1. P = polarization or plan?
2. micro = for microscope???
3. FK = photo compensation?
4. Bi = for binocular head??
5. a white engraved square, on the left when 10x magnification mark is down

[Leitzcycler]

And one more question:

6. + inside a circle (also white, engraved)

[deBult]

Some answers (from memory):

BI = Binocular with reduced variance in optical parameters: so easier to the eyes when using 2 together
FK = Projection objective for the short barrel objectives, not suitable as an eyepiece for normal viewing
P = Projection eyepiece for short barrel objectives, “old style” also suitable for normal viewing

[Tom Jones]

The + inside a circle should mean there is a crosshair reticle in place. These are mostly used on polarizing microscopes and generally cost somewhat more than an eyepiece without the reticle as they are relatively rare. They are also handy if you are trying to collimate the eyepieces in a binocular head.