You've probably figured this out, but with Rick's comment in mind, your analog gauge is off 17 points and your digital is over by 9. So if you did nothing, you would need to remember that when your analog reads 53, your 'dor is at 70%. When your digital reads 79, your 'dor is at 70%. Given of course I understand how this works and my math is correct.
salt test: 75% ideal: 70%
analog: 58% (-17 off) 53% (58+17=75-5=70)
digital: 84% (+9 over) 79% (84-9=75-5=70)