It's nice to see a Fortran code this old factored and presented properly as a subroutine! Other legacy Fotran codes are not very modular (at least this has been my experience).

The NAG Numerical Algorithm Group's FORTAN routines where fairly good and its direct descendant is still avaible.

http://www.nag.co.uk/numeric/fl/FLdescription.asp

An example of really bad use of statement labels - the convention I was taught was to use 7000 and 8000 for input and output (format statements) and to use 6000 for goto's

Start at 6000 and go up in increments of 10 or 100 and to use 6999 for the last label in a routine.

so when you wanted to exist a subroutine or function you would use GOTO 6999.

I'm not so sure about the "really bad"... I started programming in Fortran in 1973 and have never come across that convention before. Never seen any code that uses it, either, come to that ;-)

It was what I was taught when I worked at a top level Rnd company based on campus at CIT.

And we also used it at BT where Fortran 77 was used in one of the Billing systems.

It might be a more UK thing