What is the real screen size/resolution of the application that should be set?

Ionic Framework ionic-v3
1

Hello everyone,
I am developing an Android app using Ionic, and I am using a tablet that has the following resolution status:

Resolution: 1920x1200,
StatusBar height: 38px (25dip)
ActionBar height: 84px (56dip)
Application Window Size: 1920x1090
window.screen.width: 1280
window.screen.height: 800
window.devicePixelRatio: 1.5
physicalScreenWidth: 1920
physicalScreenHeight: 1200

I was developing the application using 1920x1200 and it looks awesome. But when I build the application and run it on the real device, the whole design/layout got screwed up. I kept using rem, vmin,vmax as the units.
May I ask:

  1. What is the correct resolution that I should use for development? (For Chrome developer console)
  2. Which unit should I use through out the application? Percentage is not working in some of the cases.

I would appreciate for any reply. Thank you very much in advance.