On page 417 of the Core Rulebook, it states that the DC for saving throws for magic traps is:
(DC 10 + spell level * 1.5) - so for a 4th level spell, we have DC 16 (10 + 4*1.5)
However, on page 419 we have:
for spell traps (DC 10 + spell level + ability mod). Assuming lowest ability mod, we need an Int of 14 (+2) to cast a 4th level spell, so that gives us a DC 16 (10 + 4 + 2)
But, for magic device traps, it says: DC is (10 +spell level) * 1.5. So, for the same 4th level spell we have DC 21 (10 + 4) * 1.5
So, when would the formula on page 417 apply?