This is a Dial Test Indicator (Lever Type) which offers you the following benefits: 

• Drastically enhanced durability, sensitivity and visibility.
• Glare-free flat crystal face allows easy reading of graduations. 
• O-ring seal on the bezel has the effect of providing smooth rotation and prevents dust and oil from penetrating through to the dial face.
• The stylus length is on the dial face to reorder a replacement.
• Multi-layer coatings on the crystal.