DaTuner Lite / octave 'numbers'

This is a tuner application which can be used on a smartphone. I believe that my dulcimer was tuned DAD when I bought it and I used a Snark tuner to confirm this. I have been learning to tune a dulcimer "to itself" and was given precise instructions on how to do this by an expert. I spoke to him by phone and he was very patient in answering this beginner's questions.  My DAA dulcimer had been tuned incorrectly by me and sounded awful but by following his instructions the cacophony was replaced by sounds which were delightful. So, all was good.

Unfortunately I have decided to experiment with my smartphone tuner and find that it expresses notes by using both letters and numbers and this has revealed an alarming gap in my knowledge. The letter gives the note and the displayed number is "the number of the octave".

Has anybody else used this application, please ? If so would you please tell me the pairs of letter and number that I should see when my dulcimers are tuned individually to DAD and DAA ?

Thank you.