If you are using the Polarimeter with a LabPro interface, please do the following:
1) Make sure you are using Logger Pro 3.8.5 or newer. To update your software, go to http://www.vernier.com/support/updates/logger-pro/
2) Only rotate the analyzer while data collection is active. To ensure this, allow a few seconds at both the beginning and ending of the 15 second data collection without moving the analyzer. Typically, a warning “Waiting for data…” will appear when data collection has been initiated; wait until this message has disappeared before rotating the analyzer. Rotate the analyzer two or three times, then stop a few seconds before data collection ends. You may find it helpful to add a Time meter to your screen.
LabPro users have these extended instructions because the optical encoder that tells Logger Pro what angle the analyzer is sitting on does not continuously collect data on the LabPro like it does on the LabQuest and LabQuest Mini interfaces.
For other Polarimeter troubleshooting see TIL 2591: Chemical Polarimeter Troubleshooting and FAQs