Yeoman Panama yarn

Hi
I have taken out my Passap and Knitmaster knitting machines after over 20 years. I bought from eBay June Brereton’s book of Yeoman Panama Summer Tops and have the right yarn, but the pattern says to use a reel of knit-in elastic for the rib. Do I need to use this or is there an alternative way of doing the rib?
Thanks.