Interesting explanation Henrik. I was trying to work out how 0-65535 was achieved knowing that the PIC ADC was 10 bit. Reading the datasheet

The module has five registers:
• A/D Result High Register (ADRESH)
• A/D Result Low Register (ADRESL)
• A/D Control Register 0 (ADCON0)
• A/D Control Register 1 (ADCON1)
• A/D Control Register 2 (ADCON2)
The ADCON0 register, shown in Register 17-1,
controls the operation of the A/D module. The
ADCON1 register, shown in Register 17-2, configures
the functions of the port pins. The ADCON2 register,
shown in Register 17-3, configures the A/D clock
source, programmed acquisition time and justification.
I was puzzling over the last word "justification" and the effect it would have. Now I know.