Plant and
Equipment Wellness:
Part 1 - Observing Variability |
To understand variability and
why it is a problem there is a simple tabletop game to play that is a great introduction
to the variability within processes.
In Figure 1.1 two lines are
drawn crossing at 90o with a 2mm circle drawn around their intersection.
The game is to sit at a table and drop a pen into the two millimetre diameter circle from
a height of around 300 mm (one foot). Getting a hit within the circle is the outcome
required from this process. Repeat the targeting and drop process at
least thirty times. After each drop measure the position of the new mark to an
accuracy of half a millimetre. Record the horizontal distance from the vertical line
(the x distance) and the vertical distance from the horizontal line (the
y distance) in a table like that of Table 1.1.
 |
| Figure
1.1: The Crosshair Game |
| Table
1.1: Record of the Crosshair Game Hits |
Hit No |
Distance
X |
Distance
Y |
Hit No |
Distance
X |
Distance
Y |
Hit No |
Distance
X |
Distance
Y |
1 |
8.5 |
16 |
11 |
1.5 |
5 |
21 |
1.5 |
5.5 |
2 |
7 |
9 |
12 |
1.5 |
20 |
22 |
3 |
3 |
3 |
4 |
16 |
13 |
3.5 |
3.5 |
23 |
3.5 |
0 |
4 |
3.5 |
2.5 |
14 |
2.5 |
12 |
24 |
2.5 |
6 |
5 |
5 |
24.5 |
15 |
3 |
24.5 |
25 |
0.5 |
2 |
6 |
5 |
16 |
16 |
4.5 |
6 |
26 |
1 |
2 |
7 |
7 |
10.5 |
17 |
4 |
12.5 |
27 |
3.5 |
10.5 |
8 |
5.5 |
9.5 |
18 |
5.5 |
5 |
28 |
1 |
9 |
9 |
2 |
3.5 |
19 |
1 |
9 |
29 |
4 |
14 |
10 |
3 |
2 |
20 |
6 |
4.5 |
30 |
0.5 |
3.5 |
|
|
|
|
|
|
|
|
|
|
|
|
Average |
X = 3.48 |
Y = 8.90 |
|
|
|
|
|
|
Spread |
X = 0.5 -
8.5 |
Y = 0 - 24.5 |
|
|
|
|
Observe the average and
spread, of the X and Y results.
In Table 1.1 no hits are within the two millimetre circle; some are on or
near the edge while most are well away. Even
though great effort was made to control the process, the results were across a
wide band of outcomes. This same problem
occurs in all business and operations processes. The
outcomes of a process are spread across a range of results.
That is variability. Variability becomes a problem for a business when the results
from a process are not consistently within their required boundaries.
If the aim of the game is to
have every pen-drop fall inside the 2mm circle, then we have a very poor process for
achieving that outcome. To get better results
requires changing the process. The game can be
repeated using a different process. The
results in Table 1.2 were from a process where the pen was dropped after aiming it at the
circle from above, much like dropping a bomb from an aeroplane using targeting sights.
| Table
1.2: Record of the Crosshair Game Hits Using a Sighting Process |
Hit
No |
Distance
X |
Distance
Y |
Hit
No |
Distance
X |
Distance
Y |
Hit
No |
Distance
X |
Distance
Y |
1 |
8 |
10 |
11 |
5.5 |
6 |
21 |
3.5 |
0 |
2 |
5 |
6 |
12 |
2 |
4.5 |
22 |
2 |
5 |
3 |
4 |
3.5 |
13 |
0 |
1 |
23 |
0.5 |
1 |
4 |
3 |
4 |
14 |
5 |
2 |
24 |
6.5 |
0 |
5 |
2.5 |
1 |
15 |
4 |
7 |
25 |
3.5 |
3 |
6 |
2 |
0.5 |
16 |
3 |
1 |
26 |
0 |
8.5 |
7 |
13.5 |
7.5 |
17 |
3.5 |
5 |
27 |
6 |
1.5 |
8 |
10.5 |
9.5 |
18 |
4 |
0 |
28 |
| |