The most common use of custom number formatting is to round large numbers greater than 1,000.  For example, assume we want to display 2,312,000 as 2.312.

Use the number format: 0.000,,

Each comma rounds three decimal places; therefore “,” puts your number in thousands “,,” is in millions and “,,,” is in billions, etc.  In front of the comma is where to indicate how many decimal places to show.  Note that you would want to replicate any adjustments you make on the positive side with the negative one, in case your value switches signs.  To include negative notation for the negative number syntax, format the number as: 0.000,,;(0.000,,)  Note the semi-colon (;) separating the positive and the negative formatting for the number.