Also, you specify the type of tolerance, which is one of the least important aspects of an SPC chart (which I assume you are looking for, since you posted in the SPC forum.) We need to know the process you have an the type of characteristic - length, diameter, form (roundness, parallelism). The distribution of the process - not the tolerance - is the most key question to answer. Tolerance only comes into play in SPC if you have a continuous uniform distribution. It also relates to capability - not control.