# I-Chart and X bar Chart Control limits

#### G.Pito

##### Starting to get Involved
Dear experts,
I am trying to provide a SW tool oriented to MSA and I have a simple questions:

1) Does I-Chart (individual Observation chart) need always to be associated with MR Chart? I need MR chart in order to calculate I Chart control limits UCL and LCL don't I? Does it make sense to show only I-Chart witl UCL and LCL = Mean +/- 3 sigma?

2) Same question for Xbar-chart: does it need alway R-Chart to be associated with?

Thank you for supporting a newbie #### Miner

##### Forum Moderator
Staff member
Re: I-Chart and Xbar-Chart Control limits

1) The MR chart provides redundant information and is not necessary. That is, anything unusual in the MR chart is also apparent in the I chart.

2) The R chart is necessary because it does provide information about subgroup variation that is not found in the Xbar chart.

#### Statistical Steven

##### Statistician
Staff member
Super Moderator
The short answer is you need the movR to calculate the control limits for the individual chart, even if you do not plan to chart movR values on a separate chart. Simply using +/-3S limits will give you wider limits than using 2.66*movR.

With subgroups greater than 2, the xbar and R (or S) chart is imperative as was stated, it contains useful information, as well as being able to calculate the Xbar control limits.

Dear experts,
I am trying to provide a SW tool oriented to MSA and I have a simple questions:

1) Does I-Chart (individual Observation chart) need always to be associated with MR Chart? I need MR chart in order to calculate I Chart control limits UCL and LCL don't I? Does it make sense to show only I-Chart witl UCL and LCL = Mean +/- 3 sigma?

2) Same question for Xbar-chart: does it need alway R-Chart to be associated with?

Thank you for supporting a newbie #### G.Pito

##### Starting to get Involved
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