Line and end standards plan: Introduction Line and end measurements

Figure 2.Basic length of primary line standard with end blocks
= 4L1 + 2(a + b) + 2(c + d)
Now, the combination of blocks (a + b) and (c + d) are unlikely to be of the same length. The two are therefore compared; let the difference between them be x, as shown in Fig. 3.
(c + d) = (a + b) + x


Figure 3.Comparison of blocks (a + b) and (c + d)
Substituting the value of (c + d),
4L = 4L1 + 2(a + b) + 2[(a + b) + x)]
4L= 4L1 + 2(a + b) + 2(a + b) + 2x
4L = 4L1 + 4(a + b) + 2x
Dividing by 4, we get
L = L1 + (a + b) + ½x
An end standard of known length can now be obtained consisting of either L1 + (a + b) or L1 + (c + d), as shown in Fig. 4.
The length of L1 + (a + b) is L1 + (a + b) + ½x less ½x, where (a + b) is shorter of the two end blocks. The length of L1 + (c + d) is L1 + (a + b) + ½x plus ½x, where (c + d) is longer of the two end blocks. The calibrated composite end bar can be used to calibrate a solid end standard of the same basic length.

When Precision is important?

Whenever only one measuring equipment is involved in the measurement of the dimensions, the Precision is important.

Definition of Accuracy:

• 
  The nearness to the true value is called accuracy.
  
• 
  The precise measurements made by using standard measuring equipment or non-errored measuring equipment is called Accuracy of measurements.
  
• 
  Whenever more than one measuring equipment is involved in measuring dimensions, accuracy is important.
  

They are classified as Direct and indirect measuring instruments.

1. 
   Direct measuring instruments.
   
   • 
     Graduated Measuring instruments
     
   • 
     Non Graduated measuring instruments
     
2. 
   Indirect measuring instruments.