Using this tool to test your vision,you should have a distance equal 3 meter to the iphone's screen.This tool using 0.2,0.3,0.4,0.5,0.6,0.8,1.0 to represent the vision level,which respective equal to 4.3,4.5,4.6,4.7,4.8,4.9,5.0 of the five marking standard.You could touch button at the bottom to change the level,or touch the above screen to change the test sign direction.

Using this,you can test your vision conveniently.When you feel tired,test your seeing,find whether your seeing is falled temporarily?If the answer is yes,please have a rest,this will safeguard your eye!

Thank you for your support!

Good luck!