/= Operator (C# Reference)
The division assignment operator.
An expression using the /= assignment operator, such as
x /= y
is equivalent to
x = x / y
except that x is only evaluated once. The / operator is predefined for numeric types to perform division.
The /= operator cannot be overloaded directly, but user-defined types can overload the / operator (see operator). On all compound assignment operators, overloading the binary operator implicitly overloads the equivalent compound assignment.