Well all pumps are the same whether the memory and calculator are within the pump itself or the PDM/handset. They know what the BG is, they know exactly how much insulin you've had and what time you had it hence it works out either corrections or boluses, or both, using that info.
It's now 2 hours ish since lunch so let's see - BG 11.4, then I pressed the 'Bolus' button and it told me I needed 0.4u correction, so I've had that.
Lunch was a beef sandwich but as it was 2 slices of bread from an unsliced small bloomer, I guessed at 35g carb which obviously wasn't quite enough. My pump handset shows the correction on a different line of the results screen to the any bolus amount if I've wanted to bolus too, with them added together at the bottom of same screen. I then press 'Deliver' and the pump delivers it. Presumably the Dash PDM does something very similar.
Whilst I can calculate my own boluses NP (at 1u per 10g, that shouldn't be a prob!) what I cannot do with any conviction is to calculate my own IOB right now this very minute, esp if I guessed the carb when I last bolussed. As the handset for my pump is also my BG meter and they communicate via Bluetooth anyway, I'm more than happy to just carry on doing this. I presume the Dash PDM and the Dash are something very similar.