Gentlemen:
Thank you for your help so far. I've attached a screen shot of my query so you can see what is happening (or not happening).
Now for new information: I created this database for a local research organization where I volunteer. The database contains water test results for over 9 years. My home computer runs Access 2010 and the research organization's runs Access 2007. I enter data both at home and at the research organization.
Today, I copied the database to a flash drive and took it with me to upload the new data and work at the research organization. I was talking to the research director about the problem and showed him how it worked. Surprise, surprise -- the query worked perfectly on their machine running Access 2007. At home, Access 2010 still trreats the field reference as a parameter. Glitch in Access 2010? Corruption of my program? I tried a simple query using a field reference and it works just fine at home, but using a complicated formula, it treats it as a parameter.
Unless you have any other suggestions, I will try to delete my Access Program and reload it from the original disks.
Thank you,
Tim