Measuring Techniques
D2
Part II:
Measuring the Size of a Specimen Using the
Mechanical Stage Technique
Preface:
Before beginning this module, you should
be familiar with the parts, use, and care of
the compound microscope.
 If you are unsure about the microscope’s
operation, please review the Use of the
Microscope module.
 Mishandling of the microscope can lead to
damage of the instrument.

Module Requirements:
To complete this module, the following equipment will be
provided to you by an SLC assistant.
-microscope workstation
-prepared microscope slide
-vernier caliper
-worksheet
If materials are missing or you are having problems getting
started, please ask one of the SLC staff for help.
Notes:
The Mechanical Stage method of measuring
a specimen makes use of the scales found
on the stage of the microscope. This
technique has a precision of +/- 0.1mm
regardless of the objective lens being used.
For this reason, this technique is only
suitable for measuring microorganisms that
are 1.0 mm or greater.
To illustrate how to read the scale on the
microscope’s stage, we’ll use an instrument called
a vernier caliper.
Notes:
The microscope stage uses a metric scale,
for that reason we will only be concerned
with the metric portion of your caliper.
Frequently, manufacturers design calipers
with both standard and metric scales.
Inspect the caliper you were provided with
to find its metric increments. If you cannot
find the metric portion, consult a Science
Learning Center associate.
Use of the Caliper
Notice with your calipers closed, the vernier scale
aligns with the zero on the main scale. The zero
line is called the index.
When measuring an object, its size in millimeters
can be determined by reading the number on the
main scale that is on or just to the left of the index.
In this case, the index is just
to the left of the 20mm mark.
So 19mm is our first
measurement.
Main scale
Index
Use of the Caliper
Vernier divisions
The decimal place is
found by matching up a
division on the vernier
scale which lines up with
a division on the main
scale. Here we can see
that the 7th vernier
division aligns with the
26mm division of the
main scale. Therefore,
the diameter of this pin
equals 19.7mm.
Use of the Caliper
Here are two more examples. Determine the size
of each object.
Use of the Caliper
The diameter of the penny is 19.1mm
The diameter of the MM is 13.7mm
If your answers are correct, please continue
this module. If you are unsure about your
answers please ask an assistant for help.
Use of the Mechanical Stage
The scales on the mechanical stage are used in the
same manner as the vernier caliper. Here is an
example how to find a measurement using the
mechanical stage.
1.
2.
Line up one edge of the specimen with a convenient
reference point. The edge of the field of view may be
used as your reference.
Place the specimen on the stage, and focus using the 10X
objective.
Use of the Mechanical Stage
3.
Record the initial reading. Read it the same way you
read the main scale and vernier scale on the vernier
caliper. The reading will be in millimeters.Your
readings will be taken using the scales located at the top,
or right side of the stage.
The initial reading
was at 50.6mm.
Use of the Mechanical Stage
4.
5.
Move the stage until the opposite edge of the specimen
lines up with your same reference point.
Record the final reading on the main scale along with the
vernier measurement.
The final reading
was at 60.3mm
Use of the Mechanical Stage
6.
Calculate the length of the specimen. The difference
between the final and the initial readings represent the
length of the specimen in millimeters.
Example:
60.3mm – 50.6mm = 9.7mm
Note: If your answer is negative, take the absolute value
of that number.
Try It!
Use the stage scales to measure the length of the
specimen on the slide provided with this
module.
1.
2.
3.
4.
5.
6.
Line up one edge of your specimen with a convenient reference point. The
edge of your field of view may be used as your reference.
Place the prepared slide on the stage, and focus using the 10X objective.
Record the initial reading. Read it the same way you read the main scale
and vernier scale on the vernier caliper. The reading will be in
millimeters.Your reading will be taken using the scales located at the top, or
right side of the stage.
Move the stage until the opposite edge of the specimen lines up with your
same reference point.
Record the second reading on the main scale along with the vernier
measurement.
Calculate the length of the specimen. The difference between the final and
the initial readings represent the length of the specimen in millimeters.
Module Completed!

Please return to the main desk to obtain a
post test from your friendly Science
Learning Center personnel.