Indicated size
This is the size indicated by the scales of a measuring instrument when
it is being used to measure a workpiece. The indicated size makes no
allowance for any incorrect use of the instrument, such as the application
of excessive contact pressure.
Reading
This is the size as read off the instrument scales by the operator. Errors
can occur if the scales are misread, for example sighting (parallax) errors
can occur when measuring with a rule. Vernier scales are particularly
easy to misread in poor light. A magnifying lens is helpful even in
good light and even if you have good eyesight. Electronic measuring
instruments with digital readouts overcome many of these reading difficulties.
Reading value
This is also called the ‘reading accuracy’. This is the smallest increment
of size that can be read directly from the scales of the instrument. It
will depend upon the layout of the scales. A micrometer caliper normally
has a reading value of 0.01 millimetre. A bench micrometer fitted with
a fiducial indicator normally has a reading value of 0.001 millimetre. A
vernier caliper with a 50 division vernier scale normally has a reading
value of either 0.01 millimetre or 0.02 millimetre depending upon how
the scales are arranged.
Measuring range
This is the range of sizes that can be measured by any given instrument.
It is the arithmetical difference between the largest size which can be
measured and the smallest size which can be measured. For example,
a 50 mm to 75 mm micrometer has a measuring range of 75 mm −
50 mm = 25 mm.
Measuring accuracy
This is the actual accuracy expected from a measuring instrument after
taking into account all the normal errors of usage. It can never be better
than the indicated size.
This is the size indicated by the scales of a measuring instrument when
it is being used to measure a workpiece. The indicated size makes no
allowance for any incorrect use of the instrument, such as the application
of excessive contact pressure.
Reading
This is the size as read off the instrument scales by the operator. Errors
can occur if the scales are misread, for example sighting (parallax) errors
can occur when measuring with a rule. Vernier scales are particularly
easy to misread in poor light. A magnifying lens is helpful even in
good light and even if you have good eyesight. Electronic measuring
instruments with digital readouts overcome many of these reading difficulties.
Reading value
This is also called the ‘reading accuracy’. This is the smallest increment
of size that can be read directly from the scales of the instrument. It
will depend upon the layout of the scales. A micrometer caliper normally
has a reading value of 0.01 millimetre. A bench micrometer fitted with
a fiducial indicator normally has a reading value of 0.001 millimetre. A
vernier caliper with a 50 division vernier scale normally has a reading
value of either 0.01 millimetre or 0.02 millimetre depending upon how
the scales are arranged.
Measuring range
This is the range of sizes that can be measured by any given instrument.
It is the arithmetical difference between the largest size which can be
measured and the smallest size which can be measured. For example,
a 50 mm to 75 mm micrometer has a measuring range of 75 mm −
50 mm = 25 mm.
Measuring accuracy
This is the actual accuracy expected from a measuring instrument after
taking into account all the normal errors of usage. It can never be better
than the indicated size.
