Sand Hourglasses - Factors Affecting Accuracy

The Library of Congress explains there are several factors that affect the way an hourglass filled with sand works. Paring down the factors, these are what need to be addressed in the current project of combing hourglasses with gourds:

- amount of sand 

- size and angle of the glass bulbs

- quality of the sand 

- width of the neck

- tight seal 

- level surface

In this project, the hourglasses being used were purchased from a local home furnishings store. They are glass, filled with fine sand, and are sealed shut so moisture cannot get into the glass bulbs to make the sand damp and therefore heavier.