- Discussion of ultra-cheap ($7) 150 mm “carbon-fiber” digital calipers claimed to offer 10 µm resolution and repeatability, with interest in repurposing them as closed-loop positional feedback sensors for CNC or lab automation.  
- Skepticism voiced that the housings are ordinary plastic rather than true carbon-fiber composite; YouTube teardowns were cited as evidence.  
- Technical speculation that a unidirectional carbon-fiber or fused-quartz-fiber composite frame could, in principle, achieve Invar-like low thermal expansion for metrology-grade instruments.  
- Observation that genuine zirconia gauge blocks are valued because their thermal expansion coefficient closely matches steel, enabling temperature-compensated measurements when block and workpiece are at thermal equilibrium.  
- Clarification that the sensing element in common digital calipers is a fiberglass PCB patterned with capacitive pads; true carbon-fiber boards would short the capacitive array and ruin accuracy.  
- Practical note that stock digital calipers update slowly, yet they have been successfully wired as digital read-outs (DROs) for manual mills by tapping their internal SPI-like BCD data stream.