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Arduino vs. ATMega168 Chip Pinouts
The Arduino pin names are silkscreened right on the board, but sometimes you must know the corresponding ATMega168 pin name. I printed out The Fine Manual and penciled in the Arduino names, but that’s getting smudgy.
Herewith, the ATmega168 pinout with neatly printed Arduino pin names.

Arduino vs ATMega168 chip pinouts [Update:Turns out there’s an Official Version.]
Sometimes, you also must know the relation between hardware Timers and PWM output pins:
OC0A PWM6 PWM3 OC2B OC0B PWM5 PWM5 OC0B OC1A PWM9 PWM6 OC0A OC1B PWM10 PWM9 OC1A OC2A PWM11 PWM10 OC1B OC2B PWM3 PWM11 OC2A