Bob's Fly catalog collected forecasts, sales, and demand data for $20$ items in one category from its previous catalog. The data is provided below in the table. A$/$F $135$ Forecast $1005001502103604501902807532912070505202303902501704204803403105590280148$ Sales Demand $262613551517524324332915015022422410410464644646520520240240429433275287187204462517528670374506341569480353932402701622010\mathrm{.}260\mathrm{.}270\mathrm{.}340\mathrm{.}360\mathrm{.}680\mathrm{.}730\mathrm{.}790\mathrm{.}800\mathrm{.}870\mathrm{.}910\mathrm{.}921\mathrm{.}001\mathrm{.}041\mathrm{.}111\mathrm{.}151\mathrm{.}201\mathrm{.}231\mathrm{.}401\mathrm{.}491\mathrm{.}8418\mathrm{.}380\mathrm{.}920\mathrm{.}42$ Total Average Standard Deviation For example, their forecast for the first item in the table was $100$ units, but it unfortunately only sold $26$ units. However, with the last item listed, they sold $341$ units but could have sold $569$ units if they had ordered enough inventory. For the next catalog, they have an item for which they forecast demand to be $400$ units. Suppose they will use that forecast along with the data in the above table to choose a normal distribution to model demand for this product. What standard deviation should they choose?