Opposite to other spreadsheets, calculate requires a fixed number of decimal
places for the "general" number format. The number of decimal places is
controlled using tools - Options - OOo.Calc - Calculate, "Decimal places". As a
result, numbers with a large number of digits (depending on the current cell
width) will more rapidly be represented as "##" than in other spreadsheets.

For example, with a decimal setting of 3, following number

12345.6789

might be displayed as ## in Calc (depending on the column width)

while under the same circumstances, competing spreadsheets would just display
less decimals, e.g.

12345.6

and only display ## if also the integer part doesn't fit in the cell anymore.

The latter approach allows for greater flexibility in the default display of
numbers. In Calc, a user has to recur more rapidly to adapting the cell width
(which will affect the whole column) or changing the "Decimal places" option
(which will affect the whole spreadsheet).

Thus, I would suggest that the "Decimal places" option in "Calculate"
dissappears, and that instead Calc handles the default display in a more
advanced and flexible way, i.e.

* Show the integer part and as many decimals that fit
* Even better yet for numbers that won't fit: switch to exponential format