Did you update your firmware with the Feb. 20th updates? Flex Step was added and it is accessed in Extended Settings >Expert Settings< Press: PROG - FUNC - GLOB (F3) scroll down to: [FlexStep:] ON
You do not select a step number ie 6.25 Simply enter the freq and the scanner selects the step. When you save it and it doesn't register what you entered, it will select the next closest freq that the scanner is capable of receiving. 6.25 is working on my 600.