BSON type for the » Decimal128 floating-point format, which supports numbers with up to 34 decimal digits (i.e. significant digits) and an exponent range of −6143 to +6144.
Unlike the double BSON type (i.e. float in PHP), which only stores an approximation of the decimal values, the decimal data type stores the exact value. For example, MongoDB\BSON\Decimal128('9.99') has a precise value of 9.99 where as a double 9.99 would have an approximate value of 9.9900000000000002131628….
Note: MongoDB\BSON\Decimal128 is only compatible with MongoDB 3.4+. Attempting to use the BSON type with an earlier version of MongoDB will result in an error.