Encountering difficult problems in crude fiber testing of feed, seeking expert help to answer them

Question 1: Sulfuric acid concentration: some references require a concentration of 0.255 mol per liter, while others say 0.128 mol per liter. Which one is correct? Also, why are the concentrations of sulfuric acid and sodium hydroxide used for digesting samples required to be so accurate, and why do they need to be standardized?
Question 2: What kind of device is a digestion furnace, and what are the temperature control requirements for the acid-alkali digestion process? Can the digestion device used for crude protein testing be used? Does anyone have a picture of a digestion furnace?
Question 3: Where can I find videos on crude fiber testing?