ctbiu,
After playing around with LabVIEW 5.1.1, it appears that the addition of a second scale was a new feature introduced into the graph and chart controls in LabVIEW 6i. It does not look possible in LabVIEW 5.1.1. If you need this functionality, I would suggest upgrading to LabVIEW 6.1, the current version of LabVIEW.
Randy Hoskin
Applications Engineer
National Instruments
http://www.ni.com/ask