Return value from a stored proc on error

I have an sp in SQL Server that when errors returns -4

What does -4 mean? Is there a table somewhere explaining what the possible return values are?

There must be some standard

For example

declare @RetVal int  EXEC @RetVal = stpTest  select @RetVal

where stpTest is "SELECT 1/0" returns -6.

-6 must mean something!

The sp that returned -4 only has UPDATE and SELECT INTO statements in it.

At no point does it do 'SELECT -4' so how can I "find out what -4 means in that particular stored procedure"?

Also, if there is no standard then why does a divide by zero error always return -6?

If you have an sp that does not return anything i.e. it doesn't have any select statements in it and you do:

declare @RetVal int  EXEC @RetVal = yourSPName  

Then @RetVal will have a value of 0.

If there is an error then @RetVal will be a value other then zero, for example if the only thing your sp does is "SELECT 1/0" then @RetVal will be -6.

Try it and see

My question is what do these return values mean? They must have some logical meaning!