ROK Digital Radius Gauge</a> Introduction and Function
        It is very difficult for measure the uncompleted circle by hand. or you have to buy optional instrument which cost a lot of money.  Rok measuring tools offer you a very easy and fast solution.  Equipped with digital dial indicator and five measure jaws. it is make the radius as easy as ABC.
       Features:
1. Zero Setting
2. Inch/metric conversion.
3. Data output.
4. Memory Hold
5. Large diplay.
6. Five changeable measuring jaw(10mm, 20mm, 30mm, 60mm, 100mm)
Parameter:
1. Radius Errow   △R≤0.02mm*R/s   R =radius. S=displacement.
2. Angle Error:  △R≤1
3. Battery: CR2032
Four functions:
1. Outside measurement.
2. Inside measurement.
3. Depth measurement.
4. Digital Indicator
Order No.
Range
Resolution
S error
MI-300
5-999.9
0.005mm
△S≤0.02mm

How to measure the radius of arc

            Calculates the radius of an arc when the width and height of the arc are given. The length of the arc and the angle subtended by the arc (not shown in figure) are also calculated. To draw the arc: 1)Swing arcs (using the calculated radius) below the width using as center the endpoints of the width thus creating the intersection point of the arcs. 2) Set the point of the compass at this intersection point (which now becomes the centerpoint of the arc) and swing an arc thru the endpoints of the width thus creating the arc. Take note that if the angle subtended by the arc (not shown in figure) is greater than 180 degrees then the arc length is greater than the arc length of a semi-circle. In this case, the centerpoint of the arc must be created above the width instead of below and the arc is drawn as before.
An arc is a section of a circles circumference; it can span just a tiny segment of the circumference, or a much greater portion of the circles border. One of the most commonly encountered geometric problems involving arcs is determining the radius of a circle that contains a given arc. A related problem in trigonometry is to find the angle of the sector defined by the arc.

       Such math problems can arise in manufacturing, design, landscaping, or any kind of construction based on cirlces. Luckily, it is very easy to find both the radius and the angle of a circular arc as long as you know its height and base length. You can apply the geometry and trig formulas with diagrams below, or use the convenient arc calculator on the left.  Using the Pythagorean theorem, you can solve for R by setting up an equation that involves the arc height A and half the base length B. As shown in the figure below, one leg of the right triangle has length B, and the other has length R-A.  crimp height micrometer   The Pythagorean theorem gives the equation R2 = B2 + (R-A)2, which has the unique solution of R = (A2+B2)/(2A). No trig is required to solve this problem, just algebra.