This was a fun discussion yesterday... :-)

Ok, an individual on my card yesterday made a claim. The other three of us told him he was incorrect. He couldn't prove it was true by citing a rule, but he said something like "it made sense to him."

His claim: If you do not put a mini down, and instead you throw from behind your thrown disc, you must be within 30 cm of the FRONT of your disc, since that is where the back of the mini would be... despite the fact that the technical standards allow a disc up to 40 cm in diameter.

The rules say you may leave your disc, untouched, as your marker. They also say you need a supporting point on the LOP behind and within 30 cm behind your marker. It makes no change to the rule when your thrown disc is used as your marker, yet this individual was insistent. So we said you could go up to 30 cm from the back of the thrown, untouched disc. (This is often cited as an example of smartly using the rules to help you, but he did not believe it.) Then we told him to put his money where his mouth is...

Please tell this nameless individual that we are correct and he owes Tom Coffin, Chase Rivera, and me a dollar each... :D

Yep. Dolla, dolla, dolla!

is there any place that defines what a 'marker disc' is? or what it can and cannot be?

From the 800 Definitions
Marker: A term used to indicate either the mini marker disc or the thrown disc at rest, both of which can be used to indicate the lie from which a thrower's next shot shall be played.

802.02 A. Mini marker discs shall be used to mark a player's lie as required by these rules. Mini marker discs must have a diameter of between 7 and 15 centimeters and a height not exceeding 3 centimeters.