When evaluating spirometers, prioritize measurement accuracy and repeatability in accordance with ATS/ERS (American Thoracic Society/European Respiratory Society) standards. Key specs include Flow Range (typically 0-14 L/s) and Volume Accuracy (±3% or 0.050 L). For digital models, ensure the device supports essential parameters like FVC, FEV1, PEF, and FEF25-75. Additionally, check for BTPS (Body Temperature and Pressure Saturated) correction to ensure data consistency across different environmental conditions.