Understand that a fluid is generally defined as a gas or liquid that is contained. So, a fluid can be air, water, oil, etc. So if we have a fluid in a contained space and pressure is applied to the fluid, Pascal's Principle states that this pressure is transmitted through the fluid undiminished with equal force on equal areas. The key words are equal force on equal areas. If the areas are different, the forces will be different and thus the pressures different.
Pressure is defined as force per unit area, and area is related to the diameter of the tube.
Ask your librarian to help you find a book that is less mathematical and more technical so you can get a better idea on how things work without all of the theory. Please feel free to write back if you have more questions. It sounds like a really good experiment. Thanks for using Newton. Argonne National Laboratory, Division of Educational Programs, Harold Myron, Ph.D., Division Director.