5.5 is SR5. We’ve been using the minor version number to indicate service release level in Rhino 5. So 5.4.* are builds of Rhino 5 SR4.
The version numbers have lots of good information in them, should you want to glean it:
A.B.YMMDD.hhmmb
where
A = major version
B = service release (minor version)
Y = 2010 - release year (so if Y = 3, the release year is 2013)
MM = release month (01 - 12)
DD = release day (01 - 31)
hh = release hour (00-23)
mm = release minute (00-59)
b = branch (used mostly internally to differentiate public release code streams from development streams. 5 is a release stream)
I’m curious: I go to help and check for updates, it says “This Rhino is up to date.” But then I click on “check now” and the website tells me there’s a new release, 5.5. So, question is… why does Rhino tell me I’m up-to-date when I’m clearly not?