Welcome to pprune.
Have you tried doing a search? A quick search on "ifr semicircular" in google produced more than 10000 results. Here's 3 that I've picked out.
Take a look at these links, perhaps search for a few more of you own and then if you have any specific questions post them here and you should get an answer.
happy searching
SW
http://www.nordian.net/demo_files/Fl...nning_demo.pdf
http://www.bryanweatherup.com/gouge/API/FRR.doc
http://www.pprune.org/forums/archive.../t-130347.html