Flip-Up function means if you do not need the loupe temporarily,just flip it up,no need to take it off.Adjustable nose bridge accommodates to any pupil distance and allow the user to sat your intrapupillary,Fully adjustable viewing angle allows converge and declinate angle for perfect optical alignment. .4 kinds of working distance : S(280 - 380 mm), R(360 - 460 mm), L(440 - 540 mm), XL(500 - 600 mm).How To Choose Your Loupes Determine your working distance, which will also automatically determine your field of view. While working on a friend or family member have someone measure the distance from your eyes to your friend's mouth or body: this is you working distance. Choose the distance that is closest to the selection we offer.If you are sitting while working, your height is from 160cm to180cm, we recommend working distance R (360-460mm ). IF you are standing while working, your height is from 170cm to 180cm, we recommend L (440-540mm) working distance, even XL(500-600mm) working distance will be suitable.