How often can the interest rate change on a Home Equity LOC?

Our Home Equity Line of Credit interest rate is determined by Prime Rate as published in the Wall Street Journal.  Our rate will change on the 1st day of the month following when the change is published (i.e. Prime changes and is published on 7/15/08, the new rate will begin 8/1/08).  The rate could change monthly, but Prime Rate typically does not change that often.