Roller chain can be measured relatively accurately by measuring the tight span of the drive when the drive is OFF, by measuring from center of one pin to the center of another. The more pitches (pins) contained within the measurement increase the accuracy. If the measured value exceeds the nominal by more than the allowable percentage, the chain should be replaced. The maximum allowable wear elongation is approximately 3% for most industrial applications, based upon sprocket design. The allowable chain wear in percent can be calculated using the relationship 200/N, where N is the number of teeth in the large sprocket. The relationship is often useful, since the normal maximum allowable chain wear elongation of 3% is valid only up to 67 teeth in the large sprocket. In drives having fixed center distances, chains running in parallel, or where smooth operation is required, the amount of wear should be limited to approximately 1.5%.