{"id":2511,"date":"2024-10-08T16:35:49","date_gmt":"2024-10-08T14:35:49","guid":{"rendered":"https:\/\/ellistat.com\/?post_type=guide-dutilisateur&#038;p=2511"},"modified":"2026-08-13T15:03:47","modified_gmt":"2026-08-13T13:03:47","slug":"accuracy","status":"publish","type":"guide-dutilisateur","link":"https:\/\/ellistat.com\/en\/guide-dutilisateur\/justesse\/","title":{"rendered":"Gage Linearity"},"content":{"rendered":"<p class=\"wp-block-paragraph\">Accuracy compares repeated measurements of a&nbsp;<strong>coin of known value<\/strong>&nbsp;from this true value. It distinguishes between two errors: the&nbsp;<strong>systematic bias<\/strong>&nbsp;(the accuracy deviation) and the&nbsp;<strong>dispersion<\/strong>&nbsp;(repeatability).<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">1. What you need to know:<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Visit\u00a0<strong>true value X\u2080<\/strong>\u00a0of the calibrated part; ;<\/li>\n\n\n\n<li>the\u00a0<strong>tolerances<\/strong>\u00a0minimum and maximum values of the characteristic; ;<\/li>\n\n\n\n<li>the\u00a0<strong>resolution<\/strong>\u00a0of the instrument; ;<\/li>\n\n\n\n<li>the\u00a0<strong>repeated measurements<\/strong>\u00a0on the same part, by a single operator.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">\ud83d\udca1 Aim&nbsp;<strong>at least 25 measurements<\/strong>. If the value is below 10, the study is not usable: the standard deviation calculated from such a small number of values is itself too uncertain.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The study is also being conducted&nbsp;<strong>from the gate<\/strong>&nbsp;if the measurements have already been entered there.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"964\" height=\"158\" src=\"https:\/\/ellistat.com\/wp-content\/uploads\/GageRR2.png\" alt=\"\" class=\"wp-image-4517\" srcset=\"https:\/\/ellistat.com\/wp-content\/uploads\/GageRR2.png 964w, https:\/\/ellistat.com\/wp-content\/uploads\/GageRR2-300x49.png 300w, https:\/\/ellistat.com\/wp-content\/uploads\/GageRR2-768x126.png 768w, https:\/\/ellistat.com\/wp-content\/uploads\/GageRR2-18x3.png 18w\" sizes=\"auto, (max-width: 964px) 100vw, 964px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"964\" height=\"224\" src=\"https:\/\/ellistat.com\/wp-content\/uploads\/Gage-RR3.png\" alt=\"\" class=\"wp-image-4518\" srcset=\"https:\/\/ellistat.com\/wp-content\/uploads\/Gage-RR3.png 964w, https:\/\/ellistat.com\/wp-content\/uploads\/Gage-RR3-300x70.png 300w, https:\/\/ellistat.com\/wp-content\/uploads\/Gage-RR3-768x178.png 768w, https:\/\/ellistat.com\/wp-content\/uploads\/Gage-RR3-18x4.png 18w\" sizes=\"auto, (max-width: 964px) 100vw, 964px\" \/><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">2. Statistical Results<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><span style=\"font-family: Calibri, sans-serif; font-size: 11pt; text-align: justify; white-space: normal;\">The Results tab displays each indicator with a&nbsp;<\/span><b style=\"font-family: Calibri, sans-serif; font-size: 11pt; text-align: justify; white-space: normal;\">color code<\/b><span style=\"font-family: Calibri, sans-serif; font-size: 11pt; text-align: justify; white-space: normal;\">&nbsp;: green = compliant, orange = borderline, red = insufficient. The thresholds applied are as follows.<\/span><\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><td><strong>Indicator<\/strong><\/td><td><strong>Green<\/strong><\/td><td><strong>Orange<\/strong><\/td><td><strong>Red<\/strong><\/td><\/tr><\/thead><tbody><tr><td>Number of values<\/td><td>\u2265 25<\/td><td>\u2265 10<\/td><td>&lt; 10<\/td><\/tr><tr><td>Resolution<\/td><td>\u2264 tolerance \/ 20<\/td><td>\u2264 tolerance \/ 10<\/td><td>beyond<\/td><\/tr><tr><td>Repeatability (2k\u03c3)<\/td><td>&lt; 5 % of the tolerance<\/td><td>&lt; 10 %<\/td><td>\u2265 10 %<\/td><\/tr><tr><td>A narrow margin<\/td><td>\u2264 tolerance \/ 20<\/td><td>\u2264 tolerance \/ 10<\/td><td>beyond<\/td><\/tr><tr><td>Expanded Uncertainty<\/td><td>\u2264 15 % of the tolerance<\/td><td>\u2014<\/td><td>beyond<\/td><\/tr><tr><td>Inertia<\/td><td>\u2264 tolerance \/ 30<\/td><td>\u2014<\/td><td>beyond<\/td><\/tr><tr><td>Cg and Cgk<\/td><td>&gt; 1.33<\/td><td>&gt; 1.00<\/td><td>\u2264 1.00<\/td><\/tr><tr><td>Minimum tolerance range<\/td><td>below tolerance<\/td><td>\u2014<\/td><td>higher<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>The Margin of Accuracy<\/strong>\u00a0is the difference between the average of the measurements and the true value. This is systematic error: it can be corrected.<\/li>\n\n\n\n<li><strong>Repeatability<\/strong>\u00a0is the instrument's dispersion across a single piece. It cannot be corrected by adjustment.<\/li>\n\n\n\n<li><strong>Inertia<\/strong>\u00a0combines the two into a single figure: the square root of (accuracy deviation\u00b2 + repeatability\u00b2). This is the key metric to consider when making a single decision, since a measurement error carries the same weight whether it results from a shift or from dispersion.<\/li>\n\n\n\n<li><strong>The minimum tolerance interval<\/strong>\u00a0Let's look at it the other way around: with this instrument, what is the tightest tolerance you can reasonably expect to control? If it exceeds your tolerance, the instrument is unsuitable for the part.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">3. Cg and Cgk<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">These are the capabilities of the measuring instrument, defined in the same way as process capabilities but over a reduced interval\u2014one-tenth of the tolerance.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Cg<\/strong>\u00a0looks only at the dispersion; ;<\/li>\n\n\n\n<li><strong>Cgk<\/strong>\u00a0also includes the offset from the true value.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">A normal Cg level with a low Cgk level indicates an instrument&nbsp;<strong>accurate but out of tune<\/strong>&nbsp;: to be calibrated, without changing the equipment. If both Cgk and Cg are low, this indicates an instrument&nbsp;<strong>too scattered<\/strong>&nbsp;: In that case, we need to change our approach or method.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\ud83d\udca1 The usual threshold is&nbsp;<strong>Cgk &gt; 1.33<\/strong>. The screen also displays the minimum tolerance that would ensure this threshold.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">4. The Charts<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The\u00a0<strong>accuracy graph<\/strong>\u00a0plots the measurements around the true value and the tolerance interval.<\/li>\n<\/ul>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Visit\u00a0<strong>control chart<\/strong>\u00a0shows the sequence of measurements: a slow drift is visible here, even though it is masked by the average.<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"964\" height=\"378\" src=\"https:\/\/ellistat.com\/wp-content\/uploads\/gagerrgraphique.png\" alt=\"\" class=\"wp-image-4519\" srcset=\"https:\/\/ellistat.com\/wp-content\/uploads\/gagerrgraphique.png 964w, https:\/\/ellistat.com\/wp-content\/uploads\/gagerrgraphique-300x118.png 300w, https:\/\/ellistat.com\/wp-content\/uploads\/gagerrgraphique-768x301.png 768w, https:\/\/ellistat.com\/wp-content\/uploads\/gagerrgraphique-18x7.png 18w\" sizes=\"auto, (max-width: 964px) 100vw, 964px\" \/><\/figure>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The\u2019<strong>Illustration by Cgk<\/strong>\u00a0Plots the mean, the true value X\u2080, and the bounds X\u2080 \u00b1 tolerance\/10: it visually illustrates what the number represents.<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"820\" height=\"450\" src=\"https:\/\/ellistat.com\/wp-content\/uploads\/gagerrgraphique2.png\" alt=\"\" class=\"wp-image-4521\" srcset=\"https:\/\/ellistat.com\/wp-content\/uploads\/gagerrgraphique2.png 820w, https:\/\/ellistat.com\/wp-content\/uploads\/gagerrgraphique2-300x165.png 300w, https:\/\/ellistat.com\/wp-content\/uploads\/gagerrgraphique2-768x421.png 768w, https:\/\/ellistat.com\/wp-content\/uploads\/gagerrgraphique2-18x10.png 18w\" sizes=\"auto, (max-width: 820px) 100vw, 820px\" \/><\/figure>","protected":false},"featured_media":1429,"menu_order":40,"template":"","meta":{"_acf_changed":true},"menu-guide-dutilisateur":[20],"class_list":["post-2511","guide-dutilisateur","type-guide-dutilisateur","status-publish","has-post-thumbnail","hentry","menu-guide-dutilisateur-2-gage-r-r"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.3 - 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