in today's wildly erratic markets, how likely is it that any mumufacturing company's $32 million sales target will really be that accurate? And how many manufacturers can afford to ignore the considerable impact seasons and climactic changes have on sale? Sales levels are easily influenced by the strategic actions of competitors. And then there is the unpredictability of raw material prices, currency exchange rates, and so on.
Understandably once a company's sales division sets its annual sales target, the salesr managers must come up with all sorts of ad hoc strategies fo actually reach the target. We also need to ask exactly how managers determine the merchandise turnover rate that serves as the denominator in the above formula.
Ordinarily, they use past merchandise turnover rates as their basis for calculation. They then apply various business performance indices as well as the company's current goals in determining the current year's merchandise turnover. These factors change according to the production lead-time and the yield, but they do not change as easily as the sales levels.
So, we can already see that the appropriate inventory is determined using a formula in which both the denominator and the numerator are prone to instability.
Using a formula that divides one unstable factor by another unstable factor to obtain what is treated as a stable value is like trying to divide one negative number by another negative number to obtain a positive number. To put it another way, the appropriate inventory value obtained using the above formula is only as reliable as the unreliable figures used in the formula. (See Figure 2.23)
Better that we should face the facts: Even if we take the unreliable figures for annual sales and product turnover and temper them with adjustments for estimated seasonal changes, lead-time, and profit ratios, we can still end up with an inventory level that is way off from what turns out to be actually needed