Interpreting marks on cockpit instruments

[RCnoob]

My first post...
I have been examining photos of Luftwaffe cockpits to see what kinds of supplemental information were available to pilots. I have become curious about one in particular. Many altimeters appear to have red marks at altitudes that look to me like ~300m and ~700m.

Am I reading this correctly? What would be the purpose of such marks?
Here is one that appears to have the altitudes adjustable:


In other cases e.g. airspeed, the markings are probably limit marks. For example here, maximum permissible indicated air speed at different altitudes:


I have many other questions about aircraft cockpits, especially use of checklists and procedures, but I'll save those for another message.
Thanks for any information.