Contents - Index

Continuous Input Variable Dialog Box





The Continuous Input Variable dialog box is used to enter and change information concerning a continuous input variable.  It is one of four variable dialog boxes.  The dialog controls are:
Symbol edit box:
Used to enter a unique symbol to represent the variable in equations.  It can be any combination of letters, the digits 0-9 and underscores so long as the first character is not a digit.  It can be of any length but is best limited to 1-4 characters.
Name edit box:
Used to enter a more detailed name or description of the variable.  It can be any combination of characters and any length.
Units edit box:
Used to enter the units of measure associated with this variable (optional).  Can be any combination of characters and any length.
Precision button:
Displays popup menu for specifying precision to display tolerances in this dialog box and in Summary Table window.  Default is 5 significant digits.  Can be used to specify either the number of significant digits or the number of digits after the decimal point.

TOLERANCE PANEL
Target edit box:
Used to enter the current target (or nominal).  It must be a valid constant expression.    It must be within the region specified by minimum and maximum targets on the optimization panel.  Capability studies, Pareto charts and simulations are all performed at this target.  To reference this field in other edit boxes, use the symbol "Target" or "T".
Tolerance Delta Upper edit box:
Used to enter the upper tolerance width.  Must be a valid differentiable expression which can reference the Target.  To reference this field in other edit boxes, use the symbol "ToleranceDeltaUpper" or "TDU".  The upper spec limit is equal to Target + TDU.  To reference the upper spec limit in other edit boxes, use the symbol "UpperSpecLimit" or "USL".  It must be greater than or equal to zero for all possible values of the target between the minimum and maximum specified in the optimization panel.
Tolerance Delta Lower edit box:
Used to enter the lower tolerance width.  Must be a valid differentiable expression which can reference the Target.  To reference this field in other edit boxes, use the symbol "ToleranceDeltaLower" or "TDL".  The Lower spec limit is equal to Target - TDL.  To reference the lower spec limit in other edit boxes, use the symbol "LowerSpecLimit" or "LSL".  It must be greater than or equal to zero for all possible values of the target between the minimum and maximum specified in the optimization panel.
Type of Tolerance radio buttons:
Used to specify which of the following three types of tolerances is to be used: worst-case, statistical or process.  For worst-case tolerances, only the Target, Tolerance Delta Upper and Tolerance Delta Lower edit boxes above need be entered.  For statistical tolerances, the variation panel below must also be completed.  For process tolerances, both the variation and average panels must also be completed.

VARIATION PANEL - Only displayed for statistical and process tolerances.
Distribution combo box:
Used to select distribution to use for both statistical and process tolerances.  By default, the normal distribution is selected and is sufficient for most purposes.  The exception is when the values are limited by some bound.  For example, piston radius is bounded below by zero.  Either the lognormal or gamma should be used if the values have a lower bound (See Note 1).  If the values have an upper bound, either the negative lognormal or negative gamma distributions should be used.  If the values are bounded both above and below, the beta distribution should be used.  The selected distribution determines which of the other controls on this panel are displayed.
Standard Deviation edit box:
Used to specify the standard deviation for statistical and process tolerances.  The standard deviation must be a valid differentiable expression that may include the symbols "Target", "T", "ToleranceDeltaUpper", "TDU", "UpperSpecLimit", "USL", "ToleranceDeltaLower", "TDL", "LowerSpecLimit" and "LSL".  It must be greater than or equal to zero for all possible values of the target between the minimum and maximum specified in the optimization panel.  There are further restrictions for the beta distribution (See Upper Bound).  To reference this field in other edit boxes, use the symbol "StandardDeviation" or "SD".
Cp button:
Displays a popup menu for automatically entering various equations into the Standard Deviation edit box including equations to specify a Cp of 1, 1.5 and 2, and a CV of 1%.  There are also menu items for specifying a Cp value or CV value.  These two menu items insert equations for the standard deviation with an 'X' at the place to insert the value.  Finally, there is also a menu item to specify Six Sigma quality which sets the tolerance type to process, Cp = 2 and Cc = 1/4.
Lower Bound edit box:
Used to display the lower bound for the lognormal, gamma and beta distributions.  Traditionally these distributions have a lower bound of zero.  However, it can be modified to other values.  These modifications are referred to as the three-parameter lognormal, three-parameter gamma and four-parameter beta distributions.  The lower bound must be less than the minimum target specified in the optimization panel.
Upper Bound edit box:
Used to display the upper bound for the beta distribution.  Traditionally this distribution has an upper bound of one.  However, it can be modified to other values and is referred to as the four-parameter beta distribution.  The upper bound must be greater than the maximum target specified in the optimization panel.  For the beta distribution, the upper and lower bounds result in an upper limit on the standard deviation.

AVERAGE PANEL - Only displayed for process tolerances.
Average Delta Upper and Average Delta Lower edit boxes:
Used to specify an operating window for the average.  The average must stay within the interval (Target - AverageDeltaLower, Target + AverageDeltaUpper).  Must be valid differentiable expressions that may include the symbols "Target", "T", "ToleranceDeltaUpper", "TDU", "UpperSpecLimit", "USL", "ToleranceDeltaLower", "TDL", "LowerSpecLimit", "LSL", "StandardDeviation" and "SD".  They must be greater than or equal to zero for all possible values of the target between the minimum and maximum specified in the optimization panel.
Cc button:
Displays a popup menu for automatically entering various equations into the Average Delta Upper and Lower edit boxes including equations to specify a Cc of 1/4, 1/3 and 1/2, and a +/-1.5 SD operating window.    There is also a menu item to specify a Cc value.  This menu item inserts equations for the Average Delta Upper and Average Delta Lower with an 'X' at the place to insert the value.  Finally, there is also a menu item to specify Six Sigma quality which sets the tolerance type to process, Cp = 2 and Cc = 1/4.

OPTIMIZATION PANEL
Min. and Max. Target edit boxes:
Used to specify limits for the target to use during optimizations.  They must be valid constant expressions.  The minimum must be less than or equal to the maximum.  There may be further restrictions depending on the distribution selected.  Optimizations, effects tables and plots are all performed over the region specified by the maximum and minimum targets.  The minimum and maximum may represent physical or practical limits.  In event that a response surface study was used to obtain equations for the outputs, the minimum and maximum targets should be no wider than the study region.
Include in Optimizations check box:
When this box is checked, the target for this input will change when an optimization is performed using the Find Optimal Targets dialog box.  When unchecked, the target for the input is not optimized.  By default it is checked.  Certain targets may not be adjustable in which case the check should be removed.  Other inputs may have preferred values.  By setting the input to its preferred value and removing the check, the product/process can be optimized for the preferred setting and the results compared to the overall optimum.
Dial:
The dial that appears in this window displays the position of the target in the interval determined by the minimum and maximum targets.  It can also be used to change the current target by double clicking on the desired value.
The 3-tabs represents pictorially the type of tolerance specified.  The information on the first and third tabs is similar to that displayed for an output variable in a Capability Study window.  The middle tab displayed how the tolerance would be represented on a drawing.  Two equivalent forms are given.
To close the dialog box and save the changes, click the OK button.  To cancel the changes including the addition of a new variable, click the Cancel button, press the Esc key or click the X in the upper right corner of the dialog box.  To delete the variable, click the Delete button.  For help, click the Help button or press the F1 key.

Note 1:  If a bound exists, not specifying it can lead to erroneous results.  The simulations are affected the most.  To see why, consider the case when Y = SquareRoot [X] and X has a normal distribution with a target (average) of 3 and standard deviation of 1.  Eventually the random number generator will generate a negative value of X causing an error in calculating Y.  When this happens, the program will not print any simulation results.