TOPIC #2:
GRAPHING (DENSITY AND SPECIFIC GRAVITY
CLINICAL USE OF SPECIFIC GRAVITY MEASUREMENTS)
Objectives:
By the end of today's lab session, you should:
1.
Understand the concepts of density and specific gravity, and a standard curve.
2.
Be able to perform calculations dealing with density and specific gravity.
3.
Have some
practical experience
in dealing with solutions, presenting data graphically, and determining unknown
concentrations using standard curves.
4.
Be aware of the clinical usefulness of urine specific gravity measurements.
PRESENTING DATA IN GRAPHS – GENERAL INFORMATION:
Many lab reports (in this class and in life
too) involve presentation of data in graphs, and it is important that you know how to do this properly.
Graphical
presentations are valuable because
they present quantitative data in a manner that is easier to understand and interpret
than is a list of values in a table.
This is because
relationships between the two parameters being examined can be seen
and appreciated visually in the graph.
Each graph should be neat, well organized, and easy to understand.
Your
graphs should always have:
a)
An informative title at the top.
b)
A label on each axis, including the units in parenthesis, as well as appropriate major and minor tick marks.
c)
Other information, if appropriate.
This can be inserted in any convenient blank space
on the graph.
You may
want to draw a box around it.
In some
cases,the data table and/or relevant calculations can be included on the
graph in this manner (see
example below).
The data points should be accurately placed, and should be large enough to be easily seen.
If you know the data points should theoretically fall on a straight line, draw the
“best straight line”
through all the
points.
If the origin (0,0) is a relevant data point, include this point when determining the best straight line as well.
If the data lie on a clearly recognizable curved line, draw the
best smooth curve
through the points.
If the data are irregularly situated, it may be best to
connect individual data points
.
Think
about what you want to show before you prepare your graph.
Also,
think
about the type of line or curve
expected (
what is the likely relationship between the two parameters you are plotting
) before you draw the best line
through the points.
Note:
We would like to use a
standardized format for graphing
as much as possible in this course(particularly for
linear plots – see
below).
See
Appendix 1
at the end of this exercise for instructions on making and using graphs in
Microsoft EXCEL
.
You can
get help with this during the lab exerciseif you bring along your laptop
.
Remember that a wellprepared graph is one that a firsttime reader can easily understand without additional
information
.
The graph below is a
“best straight line”
plot; a straight line coming closest to the most points is “best”
since a
linear relationship
between the two parameters (DNA concentration and Absorbance at 260 nm) is expected.
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 Fall '07
 Toews
 best straight line

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