iPod shuffles are very small and none of them have a display. There are several visual differences between generations of the iPod shuffle.  Square with circular controls — 4th Generation (2010 - 2015) Rectangular with controls along the top edge — 3rd Generation (2009) Rectangular with circular controls — 2nd Generation (2006 - 2008) Narrow rectangle with small circular controls (white only) — 1st Generation (2005) iPod shuffles model numbers are printed in small type:   A1373 — 4th Generation (The model number is printed on the part of the clip that touches the base).  A1271 — 3rd Generation (The model number is printed at the bottom of the back, underneath the clip).  A1204 — 2nd Generation (The model number is printed on the edge that is covered by the tip of the clip).  A1112 — 1st Generation (The model number is printed on the back on the iPod, at the bottom).

How would you rephrase that briefly using Vietnamese?
Nhìn vào hình dáng bên ngoài. Kiểm tra số model.