The decimal points for the displayed UCL, LCL and average relate to the number of decimal points displayed on the Y axis*.
By default, the limit labels are displayed with two decimal places in addition to the decimal points displayed on the Y axis.
You can change the number of digits displayed using the Control Limit Label Display Precision option, which specifies how many decimal places are displayed on the Y-axis.
*When you double-click the Y axis on the control chart and set "Display format" to "Fixed decimal" in the axis settings window, the description will be for the number of digits specified in "Number of decimal places."
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If you use the old control chart function from [Analysis] → [Quality and Process], you can change the number of digits to display for control limits by selecting the red triangle button in the report.
The menus for IR Control Chart, XBar Control Chart, Run Chart, P Control Chart, NP Control Chart, C Control Chart, U Control Chart, Levey Jennings Method, Pre-aggregated Control Chart, and CUSUM Control Chart available in JMP 14 and earlier have been moved to "Legacy Control Charts." In JMP 19, the "Legacy Control Charts" menu is hidden, so you must change the preferences.
