The Fluke 175 177 and 179 family has been around for some time now. I don't recall any of these meters have a "series II" designation or whatnot. Have there been significant design revisions since they were introduced? One obvious change is the LCD backlight change on the 177/179 from edge-lit green LEDs to a more uniform white color. Are there any other subtle changes that one should look for when considering when looking for a used meter in this family?