1.2 Linear Measure
and Precision
Objectives:
Measure segments and determine
accuracy of measurement.
 Compute with measures.

Segments

A line segment or
C
segment AB (or BA)
consists of the endpoints
A and B, and all points on
AB that are between A
and B. Line segments
have exact measures but
can only be as precise as
the smallest unit of the
measuring device.
Segment CD
D
l
B
A
Line
l
or AB
contains AB
Precision

The precision of any
measurement depends
on the measuring tool.
The measurement
should be within 0.5 unit
of the measure. Thus, if
AB is measured to be 2”
long, its precision is 1.5”
to 2.5”.
l
B
A
AB
Measures
Measures are real numbers, thus all
arithmetic properties can be applied.
 If we have a line segment divided into
parts, then by applying a relationship
called betweenness of points we know
the measure of each segment added
together equals the measurement of the
entire segment.
AB + BC = AC

A
B
C
Congruent Segments
When segments have the same measure,
they are said to be congruent (  ).
  is read “is congruent to.” Slashes on the
line segments also indicate the segments
are congruent.
 AB  CD

A
B
C
More About Congruency

Note, when we are discussing segments we draw a line
over the endpoints, AB, but when we are discussing the
measure of segments we simply write the letters.
Likewise, we must also be sure that when we are
comparing segments we use the congruent sign, but
when we are comparing their measures we use an equal
sign.
Never intermix the two symbols.
AB  CD
AB = CD
segments
measures
Assignment:

Geometry
Pg. 17, #12 – 39