The following code is in the middle of p. 36:
[code]if let r1 = reading1,
let r2 = reading2,
let r3 = reading3 {
...
}[/code]
That can be written more succinctly like this:
[code]
if let r1 = reading1, r2 = reading2, r3 = reading3 {
...
}[/code]
Or, equivalently:
[code]
if let r1 = reading1,
r2 = reading2,
r3 = reading3 {
...
}[/code]