Caliper trainer
EKG caliper practice
Put the calipers on the strip yourself: PR interval, QRS duration, QT interval, heart rate. We drew the strip, so we can tell you which leg was off and by how much.
The caliper trainer comes with a plan
Unlimited strips, every one explained, the caliper trainer and timed practice tests. $19.99 for 30 days. One payment, no subscription, and a refund within 24 hours if it is not for you.
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What to measure, and where the legs go
On standard paper (25 mm a second) one small square is 0.04 s and one large square is 0.20 s. Every interval is a count of small squares times 0.04.
| Measurement | First leg | Second leg | Reading it |
|---|---|---|---|
| PR interval | Where the P wave first leaves the baseline | The first movement of the QRS, up or down | 0.12 to 0.20 s (3 to 5 small squares). Longer on every beat is first-degree AV block. |
| QRS duration | The first movement of the QRS | The J point, where the trace flattens into the ST segment | Under 0.12 s (3 small squares) is narrow. 0.12 s or more is wide. |
| QT interval | The first movement of the QRS | Where the T wave is back on the baseline | It shortens as the rate rises, so it is judged after correcting for rate (QTc). At normal rates it is usually under half the R-R interval. |
| Heart rate, regular rhythm | The tip of one R wave | The tip of the next R wave | 1500 ÷ the small squares between them, or 300 ÷ the large squares. |
| Heart rate, irregular rhythm | No calipers needed | Count the QRS complexes on the 6-second strip | The count × 10. One R-R interval would give a different answer for every pair of beats. |
How the trainer works
- We know where the waves are
- Each strip is drawn by our own generator, so the start and end of every wave are known exactly. That is what lets a measurement be checked, and not just compared with a multiple-choice list.
- Which leg, and by how much
- A miss is explained leg by leg: the left one was 0.04 s late because it sat on the top of the P wave and not where it starts. The correct calipers are drawn on the strip next to yours.
- Half a small square
- A PR interval or QRS within 0.02 s of the true value is marked right; a little further out is marked close, and counts as a miss. The end of a T wave is a slope and not a corner, so the QT interval is given twice the room.
- Regular or irregular comes first
- Rate questions mix regular and irregular rhythms. Carry one R-R interval along the strip with the calipers to find out which it is, then pick the method that fits.
- Count the squares yourself
- An exam shows you a strip, not a number. Switch the reading off, use the legs as markers, count the small squares between them and type the answer in.
Simulated strips, for education and practice only. The normal ranges quoted here are the usual teaching values; at work, follow your own institution’s policy. Every strip in the trainer comes from a set that our tests have measured blind; how that is done is on the about and methods page. To name rhythms, use the practice page; to sit a whole paper, take the mock exam.