Errata: Project 1. The resistor is 150 ohm at the start of the project (parts image & text, p. 19), but becomes a 220 ohm at the end (parts image & text, p.23). The paragraph at the bottom of page 23 calculates that we need a 150 ohm resistor, but after the chart the first paragraph (page 24) says we need a 220 ohm resistor. The image shows a 220 ohm resistor
Finally, unless my eyes are deceiving me, the wiring schematic image (p.19) shows a 1000 ohm resistor.
I appreciate that you tell the reader to always wire a resistor in series with an LED -- I didn't get that from the equivalent section in the Make book. In fact, they put the LED across pin 13 and the gnd, giving the impression that resistors were optional.