CRF's Only Forums

I have a 2003, but the manual for 2004, it shows to measure the chain slack on the bottom chain, but all the videos i see show only people measuring the top chain, i assume the manual is correct even for my year, but i wanted to confirm with somebody.
it says 20-30mm in vertical play on the bottom chain

That is correct. The lower chain length is under no tension when at rest. Elevated rear wheel and recheck after torquing the rear axle nut.