So, in summary. I can just use either

NUMERIC(4,x) or DECIMAL(4,x) for small values,

NUMERIC(9,x) or DECIMAL(9,x) for big values, or

NUMERIC(18,x) or DECIMAL(18,x) for humungous values

without having to worry about problems caused by using the wrong
precision or type. Good to know! Should save me some head scratching
next time. ;-)

Thanks again,
Cheers,
Steve