Estimates & Historical Data
When Time Study fail, the “fall back” position is all too often to simply estimate production capability. Estimates (usually based on historical information) are certainly quick - but they may also be dangerously inaccurate and inconsistent.
The more that styles vary, the more inaccurate and inconsistent the estimates become. Over a period of time, estimates are based on earlier estimates, which are perhaps themselves based on historical information - so, ultimately, there is a “drift” away from reality.
Because materials, styles, machinery, workplaces and people change, estimates and historical data (which also includes everything that went wrong in the past) are simply not accurate enough and become little more than guesswork. Over time the “drift” away from reality invariably increases, and times become more and more inaccurate and inconsistent.