Cherokee ADC Standaed EKG Caliper
This caliper is exactly what you need with turdy arms for acurate measurement of tracing intervals. You haven't gotten loose over time as lesser calipers are prone to do. And the pins are also sharp and actually come together into a point. Features a chrome plated, plastic protective cover and have a point protector that built in 40 mm metric scale. A wonderful product at a good price.
Sturdy arms for accurate measurement of tracing intervals
Point protector has built-in 40 mm metric scale