Final answer:
The PR interval in an ECG tracing measures the delay in the passage of the impulse from the SA node to the AV node. If there is a delay, it will be visible in the PR interval.
Step-by-step explanation:
The question is about the PR interval in an electrocardiogram (ECG) tracing. The PR interval is the duration from the beginning of atrial depolarization (the P wave) to the initiation of the QRS complex. This interval is more clinically relevant as it measures the delay in the passage of the impulse from the sinoatrial (SA) node to the atrioventricular (AV) node. If there is a delay in this passage, it would be visible in the PR interval.