what does the number of hash symbols mean??
what does the number of hashtags define???
The hash symbol represents a placeholder for digits but only if they exist.
If you have 2 hash symbols in your custom formatting and the content of the cell is the number 1, only 1 will be displayed.
However, if you use 00 instead of 2 hash symbols, Excel will display 01 because 0s are not flexible like hash symbols.
Basically you use # to tell Excel that you want to display a number if it is available.
Regarding the number - if you don't want your decimal digits to be rounded - you need to insert more hash symbols after the decimal point.