When sourcing linear scales, the most critical factor is Resolution, typically ranging from 0.1μm to 5μm depending on the precision required for your CNC or manual machine. You must also verify the Accuracy Grade (e.g., ±3μm/m or ±5μm/m) to ensure it meets your production tolerances. Additionally, consider the Signal Output type (TTL or RS422/EIA-422-A) to ensure compatibility with your Digital Readout (DRO) or PLC system. For harsh environments, prioritize scales with an IP54 or IP67 rating to protect against coolant, oil, and dust ingress.