How to create an adjustable scrollbar to be set at variable intervals, but so far it has been having difficulties performing the separate functions

I am interested in using Sikuli to create an adjustable scrollbar to be set at variable intervals, but so far it has been having difficulties performing the separate functions. The program that I am creating a script for, which simulates internal bodily functions, has a section where I must change the external environmental pressure between multiple set intervals. There is a scrollbar with the words "Lower Body External Pressure" above it. Every time that you click the arrows at the sides of the scrollbar, the blood pressure (which starts at 0mm Hg) increases or decreases by 2mm Hg. I need to be able to tell Sikuli to lower the pressure by 2mm Hg every time that it clicks on the left arrow. The problem is that Sikuli doesnt seem to be able to find the extensions that I want it to in this situation. I have it set to find the bar that says "Lower Body External Pressure", and to then find the left-pointing arrow bellow it so that every time it clicks, the external pressure will decrease by 2mm Hg.

My question then is this: Is this a simple matter of changing up the image that I have selected for Sikuli to find or do I need to do something much more complex with the code? Is Sikuli simply having trouble finding the "Lower Body External Pressure" and left-pointing arrow windows, or does it not like how I have the code entered?

Any suggestions to this problem would be greatly appreciated. Thank you for your time!