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How to save ADF5901 calibration result and exactly why?

1.in page 24 of ADF5901 DATASHEET: "The accuracy can be improved by performing one-point calibration and storing the result in memory". exactly save what(specific place of what register)? and for what? What I understand: save resulted code, but i don't know that's location! But can't understand why to save it since by any initialization it will automatically calibrated and this calibration will improve accuracy itself, why to save?!

2. Still another question, register R9 in calibration sequence. But this register is reserved. Then what is it's uses before and after calibration. if there are used in calibration sequence then they must be defined, not to being reserved!