Please note: the physical slightly color difference or difference, does not affect the use, please do not mind, thank you! ECG 7 Step Ruler: Designed with the scientific 7-step ECG interpretation method, it provides clear, intuitive reference points for those hard to remember key points with a step-by-step follow-through process! Helps to quickly analyze ECG Portable And Transparent Design: Crafted in an ID-sized, transparent format, this family essential ecg ruler fits seamlessly into badge holders, pockets, or toolkits, ensuring quick access wherever you are-perfect for on-the-go use in workplaces, classrooms, or clinical settings Easy To Read Reference: This reference card allows you to measure the heart rate, and see if the PR interval, QRS complex, QT intervals are out of the normal range and elevation/ depression, The EKG ruler will be an excellent addition to your ID badge And High-Quality Material: Made from sturdy, transparent plastic, this 7 step ruler for ecg/ ekg is easy to clean, maintaining its clarity and functionality over long-term use in demanding environments Color: Picture color Material: plastic Package Contents: 2 * ECG 7 Step Ruler 2 * blue boxes Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.