USER'S GUIDE - ShipWeight

Estimating Weight and CoG
3.6 Taking uncertainty into account
In the estimation area, the right-hand column contains information about the
standard deviation. The standard deviation can be given either as an absolute
value or as a percentage. To switch between these ways of showing the
uncertainty, select the Std. Dev. in the estimation dialog.
The deviation of the selected estimation coefficient is calculated from the
spread of the coefficients around the regression line. If the number of
coefficients is less than three, the deviation cannot be calculated. Then a
value based upon subjective judgment can be manually entered into the grid.
If some of the other parameters are uncertain, an uncertainty value should be
entered into the grid to the right parameter value. When all parameters have
got appropriate uncertainty value attached, pushing the Calc.std.dev button in
the estimation area gives the total uncertainty for the weight in this weight
group, and this value is stored.
By the use of successive calculation the uncertainty for a weight group
containing subgroups, will be calculated on the basis of the uncertainty of the
subgroups.
Even though the uncertainty is an approximate method to obtain the
uncertainty for a weight and even if you have to set the values yourself for
most weight groups, there are several reasons to take the uncertainty into
account. First of all you will be able to use your resources where they are
most needed. When selecting Most uncertain under the Std. Dev. menu in the
main window, ShipWeight will take you to the weight group where a further
estimation and splitting of the group will give the greatest impact on the total
result. This will help you to focus on the weight groups that really matter at
any stage of your estimation. Secondly, taking uncertainty into account will
give you a basis to compare the uncertainty between different projects.
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ShipWeight – User’s Guide, version 10.0, April 2011