Analog prescale question

I'm using a nRF51844

I'm writing my own ADC reading routines because I can't find any examples, but I know how to code so that's not a problem. I just want to confirm something:

If the analog reference is selected to be ADC_CONFIG_REFSEL_SupplyOneThirdPrescaling , then does that mean to get a one-to-one reading, I should be using ADC_CONFIG_INPSEL_SupplyOneThirdPrescaling as well? If I do this, I assume that if my VDD is 3.3V and input is 3.3V, I get a 10 bit reading of 1023, correct?

What are the tolerances on the two prescalers?