This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The time to give a patient the next dose of medicine can be set on the indicator, as shown in the sketch, and retained without fear of its being changed until the dose is again given. The indicator consists of a strip of paper which will reach around the bottle neck and is divided into 24 equal parts representing hours and half hours. The paper is then pasted to the bottle neck. An ordinary pin is then pushed into the cork as shown. After a dose of medicine is given to the patient the cork is replaced so that the head of the pin will indicate the time for the next dose. By this method, an accidental shifting of the indicator is almost impossible.