In Chinese manufacturing, QC is the biggest variable between suppliers. The difference between a ¥60/hour and ¥120/hour CNC shop is largely in their measurement capability.
Standard temperature: 20°C. Every 1°C change = 1.2μm length change on a 100mm steel part. A 35°C summer workshop vs 5°C winter gives 36μm difference — enough to fail a ±0.05mm tolerance part.
Rule of thumb: measurement tool accuracy must be 1/3 to 1/10 of the part tolerance.
Steel ruler → 0.5mm, for layout. Caliper → 0.02mm, general measurement. Micrometer → 0.01mm, precision diameter. Dial indicator → 0.001mm, runout and alignment.
Digital calipers: ¥50-100 in China. Imported Mitutoyo: ¥500-1000. Digital is good enough but unreliable in high humidity (most workshops are humid). Mechanical calipers never need batteries.