Dear Experts,
I which case we have to use XmRTrend chart?
Many thanks.

They are generally used when n=1 and the sampling frequency is relatively low.

It is recommended for continuos process, like chemical batchs.

The subgroup of 1 is used for the case when 1 is the rational subgroup of the sample (you shouldn't agrupate the data in a 5 points sample just because you want to use a subgroup of 5, the points must have a relationship which differ form the next group of data, so there is a within and between sample variation).

But XMR with trend is used when there is a lineal trend change in the data, Don Wheeler put it into the article

http://www.spcpress.com/pdf/Selden.pdf

Dear Experts,
I which case we have to use XmRTrend chart?
Many thanks.

Here is a chart selection tree you may find usefull.

Data Analysis Chart Selection Tree.doc (http://elsmar.com/Forums/attachment.php?attachmentid=2777&d=1097504213)

Dave

Use the XmR Trend chart when you believe there is a trend in the data caused by environmental factors (e.g., inflation causes rising costs).