usability testing for using Ipad

FINDING THE CLAY CONTENT BY HAND
In the following instructions you will learn how to estimate the percent clay content 0 a
soil sample using the A method called the hand ribbon.
WARNING: YOUR HANDS WILL GET DIRTY.
1. Gather all equipment necessary (Figure 1). You will need a water source (a cup with water in
it will work fine), and a tape measure or ruler. Other optional equipment you might consider is
some paper towels and a tool for loosening hard soil (a hand trowel, or knife will do the job).
Figure l.
Depicted are the tools you will need, a water bottle, and tape
measure. The optional equipment consists of the .paper towels and
tools for loosening hard soil such as the hand trowel, knife or
hammer.
2. Select an area of soil for testing. Try to find a spot that is relatively free of organic matter and
debris such as rock.
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3. Loosen the soil so that you are able to grab about a hand full of it for testing (figure 3).
Figure 3.
4. When you have about a hand full of soil in your hand, pour just enough water over it to make
it soft and pliable (Figure 4.1). A good way to tell when you have enough water is that when you
squeeze the soil only a few droplets fall from your hand (figure 4.2).
~,;……—-.—–.-.-.——–
Figure 4.1
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5. Kneed the soil in your hand for about 5 to 10 seconds in order to make the soil workable.
When done you should have a ball of soil in your hand (figure 5).
Figure 5
‘7——-·—–
6. Start to press the soil together pushing your thumb into the soil so that it comes out the top of
your hand and starts to form a ribbon, or strip that is about 114of an inch thick (figure 6.1). Keep
pressing the soil through until the ribbon of soil falls off from the main sample source (figure
6.2).
_ _ ~ ‘” .’ ‘~T.~~ ‘:~~~’.
~- ,”
7. Measure the length of the ribbon of soil that broke off (figure 7). It is estimated that for every
inch in a ribbon of soil, there is about 10% clay content. So if you have a ribbon of soil that is
two inches long, it has a clay content of about 20%.
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Figure 7. The soil shown has an estimated clay content of 10%.
Congratulations! You now know how to estimate the clay content in soil. You can use this
new skill to expand your knowledge of the many different soil types that are under our feet
every day.
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USABILITY TESTING FOR FINDING CLAY CONTENT BY HMlD
Soil science majors and minors
INTRODUCTION
A usability test was preformed on the set of instructions I wrote called, “Finding the Clay
Content of Soil by hand”, in order to find parts to improve, and re-write before final
submittal. The method for finding clay content that I used is called the ribboning
technique. The reason it is called this is because you form a “ribbon” or strip of soil with
your hand during the test. This is a useful test for a soil scientist to use in the field to
quickly determine an estimate of clay content in a soil sample. From the clay content the
scientist can then determine other factors like the cat-ion exchange capacity, and the
aggregation potential of the soil.
Soil samples for the test were collected out side of my house located on nw 8th street
Corvallis Oregon on February 23rd 2015. The soil taxonomic class was found online from
the Natural Recourses Conservation Service (NRCS) soil survey of Corvallis Oregon.
They categorized the soil as Amity silt loam. From this site I also obtained the actual
percentage of clay in the soil.
TESTING PROCEDURES
A total of 6 tests were preformed including a test preformed by myself. I monitored each
volunteer as they preformed the test and took notes and wrote down their results in the
testing log.
LOCATION
4 out of the 6 tests were preformed at my house located on NW 8th street Corvallis
Oregon. The other two were preformed at my girlfriend’s house located on 23rd street. At
both locations we preformed the test outdoors so that we wouldn’t get any dirt inside the
house.
METHOD
I told each of the volunteers that they would be handed a set of instructions and they had
to attempt to complete the task. Before they started the test I warned them that they are
dealing with dirt, and it will be dirty. I supplied all the tools necessary to complete the set
of instructions. Because the soil sample was already given to them the only tools that they
needed were a water source and a tape measure.
As the volunteer carried out each step of the instructions I observed them and wrote down
notes about which part of the test was the hardest for them. When they were done with
the last step I had the volunteer tell me what their estimation of clay content in the soil
sample was. I recorded their answers on a table of results that I made on an excel work
sheet. I then took a percent error from the estimated’ clay content compared to the actual
clay content displayed from the soil survey.
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When the volunteer was finish I handed them a paper towel and more water to wash their
hands with and thanked them for their time.
RESULTS
DATA
The results of the hand clay test are displayed on Table 1. The most common estimate
for percent clay was 15% , the lowest guess was 10%, and the highest was 20%. In the 5th
column of the table the percent error is displayed. The percent error is found by
subtracting the actual clay content from the estimated, and the dividing by the actual clay
content again. The average percent error for the hand test was 32.5%.
Table 1.
Imported from excel work sheet
PERCENT PERCENT
CLAY CLAY PERCENT
NAME SOIL TYPE ESTMATED ACTUAL ERROR Comments
Russell Amity Silt Loam 10 21.0 52.4 the intial test I preformed
understood test well, has
preformed test before in
Jordan Amity Silt Loam .15 21.0 28.6 class.
had trouble understanding
Kurt Amity Silt Loam 15 21.0 28.6 the ribbon part of the test
Preformed test well,
MyTrang Amity Silt Loam 20 21.0 4.8 commented on first picture
had toask for clarification
Danni Amity Silt Loam 10 21.0 52.4 in ribboning section
Ryan Amity Silt Loam 15 21.0 28.6 preformed test well.
MODE 15 AVERAGE 32.5
COMMENTS
The most common comment was that step 6 is a little hard to follow. The pictures do help
but the volunteers were still a little confused and one needed help. Another comment was
that the first picture shows all the tools necessary and optional, the volunteer stated that it
might be better if there were two pictures, one of the necessary tools, and another of the
optional.

A percent error of 32.5% is to be expected in the results of the test. The reason for this is
because fining the clay content by hand is only a rough estimate of the. actual percentage
of clay in the soiL Testing in a lab would achieve results with a lower percent error.
CHANGES TO INSTRUCTIONS
The wording to step six has been changed so that it is a little more descriptive, the format
the words under the first picture were changed to make it easier to follow. I added an
introduction to the beginning followed by a clear warning to the user that their hands will
get dirty. At the end of the instructions I put a remark congratulating them on their
successfully completion.
RECOMMENDATIONS
For future testing it would be easier to find a time where I could test multiple people at
once. It also could give better results if I had’ the volunteers test multiple soil samples of
different taxonomic classes.
CONCLUSION
In summery most volunteers were able to complete the set of instructions with out major
difficulty, this result has provided the conclusion that the set of instructions are easy
enough to follow to complete the task. The only problem with the test was step number 6.
To fix the problem this step was re-worded so that it was a little easier to understand.
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Finding the Clay Content of Soil by Hand
USABILITY TESTING LOG 2/23112
Table inserted via excel workbook.
PERCENT PERCENT
CLAY CLAY PERCENT
NAME *SOIL TYPE ESTMATED ACTUAL ERROR Comments
Russell Amity Silt Loam 10 21.0 52.4 the intial test I preformed
understood test well, has
preformed test before in
Jordan Amity Silt Loam 15 21.0 28.6 class.
had trouble understanding
KLirt Amity Silt Loam 15 21.0 28.6 the ribbon part of the test
Preformed test well,
MyTrang Amity Silt Loam 20 21.0 4.8 commented on first picture
had to ask for clarification
Danni Amity Silt Loam 10 21.0 52.4 in ribboning section
Ryan Amity Silt Loam 15 21.0 28.6 preformed test well.
MODE 15 AVERAGE 32.5
NOTES
The actual percentage of clay was found by looking on websoilsurvey.nrcs.usda.gov.
This is a site that is part of the Natural Resources Conservation service.
* The soil type may be a mixture of Amity silt loam and Woodburn silt loam due to a
sample site location on the border of a change in soil type (according to the local soil
survey), however, this shouldn’t effect the clay content in they soil because both soil
classes have the same percentage of clay.
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