In "Hogarthian" diving it is... and fancy that... we're in the Hogarthian forum!
Ok, I don't use a 5' or 6' or 7'. But I can't find a reference anywhere that says 5' for a single tank in open water. Everywhere I read is 7' for overhead environments and 5' for single tank shallow dives. Give me a reference an I'll be smarter.
tnx don O