Your handset must be on new 3.6 firmware level as that now supports 29 functions (F0 - F28). The F symbol is no longer used - instead you use the + and - keys to switch between 3 function groups. Vertical bars are displayed to show which of the 3 function groups you are using at the time. All of this is in the 3.6 version of the manual which you can download from the Lenz web-site.