I have a 178C and cannot remember how to convert the nm and knots to miles and mph. Also, how does one bring up present position in Longitude and Latitude? I have read the manual and cannot find answer there or on Garmin's website.
Don't know if this will help but I have a 276C and under the menu options there is a page for map setup. In that choice there is an option for the units (knots, miles, etc) that you want displayed. Make your selection and the machine does the rest.