+ :title [choosing drill bit]
+ (p [the arduino comes with holes in it already, so we will make
+ some choices around those holes.
+ choosing the right drill bit depends on what job you are
+ doing.
+ right now, we are making holes for screws to hold the
+ arduino to the deck.
+ there are two constraints between the hole and screw.
+ each hole needs to be big enough for the screw body to fit
+ through it.
+ the holes also need to be smaller than the screw's thread.
+ since there are holes on the arduino already, the screw was
+ chosen to match it.
+ the screw was chosen so that the hole on the arduino was
+ bigger than the screw body and smaller than its thread.
+ we will choose the biggest drill bit that fits through the
+ hole on the arduino, then use that to drill holes in the
+ deck.])
+ (p [here's a cross section of a screw in the deck]
+ (figure :legend "screw cross section"
+ (image :file
+ "arduino-to-deck/screw-cross-section.png")))
+ (p [check
+ ,(itemize
+ (item
+ [what would happen if the drill bit were larger than the
+ screw thread?])
+ (item
+ [what would happen if the drill bit were smaller than the
+ screw body?]))]))