Rcu-014 is your model number for your keyboard/trackball. Maybe some quality time wit your manual is in order. The performance monitor function is required on vessels over 300GT on international voyages. It’s preset and no arc in the distance specified is telling you that you have a greater than 10db loss and your magnetron is bad. That’s section 1.47.2 in the furuno manual for the 21/28’s. Dust your manuals off and see if you can find some wording to that effect.