97. The most practical method of determining the condition of a shaft bearing while the shaft is in operation is to __________.

Monitoring lube oil temperature is the most practical method for assessing a shaft bearing's condition during operation because bearing distress initially manifests as elevated oil temperature. This is readily achieved through existing temperature gauges or thermocouples, providing continuous and safe condition assessment, unlike oil viscosity or contamination tests, or visual inspection which are impractical or unsafe during operation.