Article: iPod Nanos have been released in five major different forms. This can give you a quick idea of how old yours is.  Rectangular with touch screen — 7th Generation (2012 - 2015) Square with touch screen — 6th Generation  (2010) Rectangular with click wheel — 4th and 5th Generation (2008 - 2009) Wide screen with click wheel — 3rd Generation (2007) Small screen and click wheel — 1st and 2nd Generation (2005 - 2006) You can find the iPod Nano's model number on the back of the iPod itself, near the bottom. The following model numbers correspond to the following generations:   A1446 — 7th Generation  A1366 — 6th Generation  A1320 — 5th Generation  A1285 — 4th Generation  A1236 (The serial number also ends with YOP, YOR, YXR, YXT, YXV, or YXX) — 3rd Generation  A1199 — 2nd Generation  A1137 — 1st Generation

What is a summary?
Look at the form factor. Check the model number. Compare the model number to a generation.