The cache is guarded by a 4 reel combination lock. There are two codes you need to figure out to get to the logbook, the first is:
(1)Reel D is an even number
(2)Reel D plus reel A = 7
(3)The digits total 22
(3)Reel C multiplied by reel A = 42
You might want to bring some paper to work out the codes. Please be careful to ensure you put all contents back into the correct places.