Historical fact about NN Savitsky

Dr. Savitsky had the same initials in the name as my father, NN (рус. Савицкий НН). Coincidentally my current city is NN (Nyzhny Novgorod). In 1956, Dr. Savitsky used an intersting method of graphical analysis of the pulse wave.

The method was as described below:

Paper tape and ink pulse waves recordings were increased with an overhead projector and copied on 1 mm-lined paper. Then a series of points on the wave were marked in accordance with the specified time periods. Wooden square was applied to these points along a tangent, as shown in the picture (left). This made possible obtaining the first derivative, as shown on the right.

Colleagues, please let me know if you are interested in citations on the subject. I am very pleased to share this information with you.

Best regards,
Dr. Posokhov