Explain terminology please

[NOTTNICK]

Hope you don't mind this as a new post as I queried cutting earlier:
My quote for the sawn board says:

Green Western Red Cedar No2 Clears & Better allowing 15% No4 – Machined

I gather that No2 is reasonable quality, but what does the rest mean? Can someone help please.

 

[NazNomad]

https://www.google.co.uk/url?sa=t&rct=j ... j04h3jtWig