It's pretty simple, your reference altitude has to be set to zero and your Barometric Pressure is set to sea level.
If you watch your altitude, or even DA using a kestrel, you'll see it constantly adjust, not big, but it moves, if you walk out your door in the morning it will give you one altitude and if you walk out later it will read slightly different again. It's because it uses Air Pressure.
Air Pressure, Air Density, is all the bullet cares about. The reason Density Altitude works is, it's where the bullet "thinks" it's at. So while the actual altitude might be 5000ft above sea level, given the conditions it would appear it is at 8000ft or even 2000ft, that doesn't mean that is the actual altitude but it represents a number that works when shooting.
When using battery-less charts, to get your DA you use the altitude you are at, along with the temperature. However depending on the conditions outside and where you are in the world, those numbers can be off by 1000ft DA or more. It's "good enough for government work" is the term. Using Altitude and Temp is a shortcut, using a meter, you want to use the actual DA as noted or if you are using a ballistic computer you use the Absolute Pressure... which mean you don't use Altitude.
I would not use corrected pressure with any ballistic computer, ever... the only time you can consider it, is if you are sitting in a hotel room with no clue what the actual Barometric Pressure is and you have to go by the newsman who is giving your corrected pressure. Then you need altitude.
Programs were not designed to use DA, that was added much later and not all programs allow you to use DA, so why get in the habit. They were written to use the actual data, not shortcut data. If you have a kestrel, use the actual values with the reference altitude set to 0, and the BP set to 29.92. You can record your DA in your log book, but use the real numbers.
