What are the correct Parallax Slider width sizes when using on a Bootstrap3 responsive websites for the four viewports "xs", "sm", "md", and "lg"...?
Since percentage widths are not available, I have two problems:
(1) I cannot get it to center on certain screens sizes.
(2) Width size either too small or too big -- for instance on the iPhone ... in regular upright portrait position, the small 280px width works well, but when I turn the phone sideways (landscape), the Parallax Slider seems just to small on the page.
URL: dm-webcreation.com/airpyramid/
Thanks for all your help!

Any suggestions? In Bootstrap 3, are there more viewport sizes that can be added than just the four (xs,sm,md,lg)?

Hello David,
There are no any "correct" sizes that should be used, it is up to you to decide how you would like your slider to look on the page.
There are no any different sizes that xs,sm,md and lg.
By the way, in my own projects i prefer not to use image sliders on phones, but instead i use responsive images.

www.minimit.com/articles/tips-resources/bootstrap-3-responsive-grid-psd-templates

use these photoshop psd templates to create the "correct size" graphics for the responsive design....