[saurik]

The nonce used for ECDSA signatures is not the same as the nonce used for Ethereum signature. The term "nonce" is a general term that is used in any number of systems to mean a value which should only be used once, and might apply to any number of layers or protocols in a given system.

There are various techniques people use for them: a careful counter, a precise timestamp, a hash of the rest of the data, or a random number. Often you can choose as the user... as long as you don't use the same value twice; alternatively, your choice of nonce might be verified by your counter-party (as with Ethereum's account nonces).

The consequences of using the same value twice will also differ: your request might be rejected/ignored, you might be penalized or cause an error, it might expose your identity to a system where you were otherwise anonymous, or it might allow someone to calculate your private key. The high-level idea is what matters, not the specifics.