Spotlight: Calculated Industries QR Calc <Title>
Quick Facts
Model: 3375
Name: QR Calc
Company: Calculated
Industries
Timeline: 1993
Type: Quality Control,
Statistics
Operating System:
Algebraic
Digits: 7
Memory: 1 general
purpose memory register plus specific variable registers
Power: 1 CR-2032
battery
When I purchased the QR
Calc, there was no manual with it. Normally, it wouldn’t present
any issues because I can often find manuals online. That is not the
case with the QR Calc. If there is any manual online, please email
me. I’ll have to be more careful next time.
I apologize that I will
not be able to describe all the functions but hopefully I describe
enough features to give the reader a general idea. Please check out
the sources below.
Features
Let’s start with the
mathematical functions included: powers and roots (y^x, x². √),
natural logarithm (ln), exponential function (e^x), reciprocal (1/x),
arithmetic (+, -, ×, ÷), and the standard percent key which
operates they people expect it to (%). The order of operations is
enforced. Like a lot of calculators, the change sign (+/-) key is a
shifted function.
The operating range of
the calculator is 7 digits: -9,999,999 to 9,999,999. Any calculator
that has a result outside of this range causes the QR calculator to
display an error message.
The store key for the QR
Calc is labeled [ Set ].
The function →PPM
changes any number into n parts per million.
Example: 0.0014 →PPM
displays 1,400 PPM.
Here are some functions
I was able to find out and figure out:
Normal Distribution
The normal distribution
functions calculate areas of the standard normal distribution,
assuming that μ = 0 and σ = 1.
n [ nZ ]: lower tail
probability (from -∞ to x = n)
n [ 2nd ]
(ModZ): probability from x = 0 to x = n
One Variable
Statistics
The QR handles a single
set of statistics with the following key and key sequences:
[ Add ]: Add a data
point (Σ+)
[ 2nd ] [ Add
] (Subtract): Subtract a data point (Σ-)
[ 2nd ] [ + ]
(S←→P): Toggle between standard deviation and population
deviation (σn indicator)
[ x-bar ]: Calculate
the arithmetic mean.
[ R ]: Calculate the
range of the data.
[ 2nd ] [
x-bar ] (N): Calculate the number of data points.
[ 2nd ] [ R ]
(σ): Calculate the deviation, depending on the deviation mode set.
[ Low ]: Returns the
minimum value of the data set entered.
[ 2nd ] [ Low
] (High): Returns the maximum value of the date set entered.
[ Skew ]: Skew. I’m
not sure what formula the QR Calc uses because I have not been able
to match results with any formula I found yet.
[ 2nd ] [
Skew ] (Kurt): Excess Kurtosis. Kurtosis measures how concentrated
the data is with respect to the mean.
The formula used for
Excess Kurtosis:
μ4 = 1/n * Σ((xi –
mean)^4)
kurtosis = μ4/s^4 – 3
Process Capability
Indices
If a process is mature,
that is a process that is regular and has been executed for a period
of time, we can measure the capability index.
There are two capability
indices:
Cp: for a centered
analysis
Cpk: for a non-centered
analysis. This metric is used for potential future performance.
Generally, we want these
indices to be at least 1. Capable processes have an Cp index of
1.33 or higher.
Key strokes:
Enter the mean: [ Set ]
[ x-bar ]
Enter the deviation: [
Set ] [ 2nd ] [ R ] ( σ )
Enter the lower
specification limit (based on the normal distribution): [ Set ] [
LSL ]
Enter the upper
specification limit: [ Set ] [ 2nd ] [ LSL ] (USL)
Each variable entered
will have an indicator.
Calculate Cp: [ 2nd
] [ Cpk ] (Cp)
Calculate Cpk: [ Cpk ]
Example:
LSL = - 1, USL = 1,
mean = 0.05, deviation = 0.27
[ 2nd ] [ ×
] (AC) to clear out the registers if needed
0.5 [ Set ] [ x-bar ]
(x-bar indicator is on)
0.27 [ Set ] [ 2nd
] [ R ] ( σ ) (σ indicator is on)
1 [ 2nd ] [ -
] (+/-) [ Set ] [ LSL ] (L indicator is on)
1 [ Set ] [ 2nd
] [ LSL ] (USL) (U indicator is on)
Results:
Cp: 1.234568
Cpk: 1.17284
That is a pretty good
process.
Formulas Used:
Cp = (USL -LSL) / (6 *
σ)
Cpx = min((x-bar –
LSL) / (3 * σ), (USL – x-bar) / (3 * σ))
Control Charts
We get to the main
feature of the QR Calc: Control Charts and Capability Limits. On
the back of the calculator, the QR Calc has a list of handy formulas.
The heart of the QR Calc
is the table of constants that are used in control charts and limit
charts. Often the chart limits are built on many samples of n data
points each, where x-bar is the average of the sample averages, and R
is the average of the range samples. We can also build chart limits
with one sample. The QR Calc can only handle sample sizes from 3 to
25 data points.
Mean Control Chart
Limits:
Lower: LCL-mean = x-bar
– n * A2 * R
Upper: UCL-mean = x-bar
+ n * A2 * R
R Control Chart Limits:
Lower: LCL-R = n * D3 *
R
Upper: UCL-R = n * D4 *
R
A2, D3, and D4 are
constants used in calculating control chart limits. Accessing these
constants takes one argument, which is the sample size.
The A2 constant for a
sample size of 3: 3 [ nA2 ] returns 1.023.
Below is a short table
of constants, as determined by the QR Calc.
Sample Size n
|
Constant A2
|
Constant D3
|
Constant D4
|
5
|
0.577
|
0
|
2.114
|
10
|
0.308
|
0.223
|
1.777
|
15
|
0.223
|
0.347
|
1.653
|
20
|
0.18
|
0.415
|
1.585
|
25
|
0.153
|
0.459
|
1.541
|
Standard deviation can
be estimated by using the average range ( R ) and another constant
d2:
σ ≈ R / d2
Sample Size n
|
Constant d2
|
5
|
2.326
|
10
|
3.078
|
15
|
3.472
|
20
|
3.735
|
25
|
3.931
|
A table of constants
from n = 2 to 25 can be found here:
https://sixsigmastudyguide.com/x-bar-r-control-charts/
Example:
Construct
mean and range charts from a sample (n = 5):
3.995
|
4.26
|
4.37
|
4.44
|
4.58
|
Keystrokes:
(after
clearing data)
3.995
[ Add ] 4.26 [ Add ] 4.37 [ Add ] 4.44 [ Add ] 4.58 [ Add ]
X-bar
chart:
LCL:
[ x-bar ] - 5 [ nA2 ] [ × ] [ R ] [ = ] Result: 3.991455
UCL:
[ x-bar ] + 5 [ nA2 ] [ × ] [ R ] [ = ] Result: 4.666545
R
chart:
LCL:
5 [ 2nd
] [ nD4 ] (nD3) [ × ] [ R ] [ = ] Result: 0
UCL:
5 [ nD4 ] [ × ] [ R ] [ = ] Result: 12.36669
The
QC calc has contains the E2 constant.
Final
Thoughts
The
functions that I still do not know about or have figured out are:
TRGa, TRGb, RS a, RS b, %Low, and %High.
This
review is incomplete. I will keep searching for a manual, I may have
to buy another QR Calc.
This
calculator is a rarity, and one worth checking out.
Sources
Hessing,
Ted. “Process Capability (Cp & Cpk)” 6σSTUDYGUIDE.COM
(no specific date give, first comment on November 19, 2014)
https://sixsigmastudyguide.com/process-capability-cp-cpk/.
Accessed January 2025.
Hessing,
Ted. “X Bar R Control Charts” 6σSTUDYGUIDE.COM (no specific
date give, first comment on April 17, 2018)
https://sixsigmastudyguide.com/x-bar-r-control-charts/.
Accessed January 2025.
Hewlett
Packard. HP-65 Stat Pac 2 Cupertino, CA.
https://literature.hpcalc.org/items/975
1975
Next
time, I’m going to see if a manual comes with it. Not everything
has a manual online.
Eddie
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original content copyright, © 2011-2025. Edward Shore.
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