The short-term z-score, Zst, is a short term capability metric or short term sigma level, calculated using short term data. It is calculated using the function: (Spec limit - Short Term Mean)/Short Term Std. Dev. Short term data is obtained by sampling in a very limited period of time when the input Factors remain constant. If calculated after an improvement action has been put in place, short term data takes into account only common cause or random variation. Zst is related to the long term z-score through the function: Zst = Zlt + 1.5.