Hello,
Here are a few screenshots to show the setup of our Demo Slider.

Form:
	 
"Population" Field Storage:
Field Name = city_population (you'll find a ref. below)
	 
Search Type > Button 1:
	 
Search Type > Button 3:
As you can see a 2nd field with the exact same storage "city_population_2" is needed here (you'll find a ref. below)
	 
"Slider" Field:
	