I've attempting to develop a control chart with lower control limits and I believe I'm calculating everything correctly. This is all force data. There is a minimum force no maximum.

Because of the huge range difference from my max pulls I believe my Standard deviation is being thrown off and in turn making my control limits larger then they should be.

Is there supposed to be a different way I calculate lower control limits when there is only a minimum, or is this the correct / only way to do it, and in turn its telling me my process is out of control since the limits are calculating below the spec limit.

Nothing measured below the spec, but the calculated lower limit is well below the spec.

Just so numbers are available.

Spec min is 20. My lowest reading is 23, highest is 60 mean is 32 with a current stdev of 7.75.

My LCL is 8.96 and UCL is 55.44 (which I don't have a limit for).

If I remember correctly, doesn't this tell me I'm not only still in control under 20 ft lbs, but that statistically I could get a reading below 20?