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Again, you haven't gone into any sort of detail about anything regarding these dropdowns so I have no idea what it is you need to do. Besides... use Javascript? If you want more detailed advice then you'll have to start posting code and markup and whatever you have, along with a complete description of what sort of "data matching/comparison" you're talking about.

It's not like the experience is entirely unusable... Make the scanner so it gets the data from the QR code. Use Javascript to do whatever it takes to validate with the dropdowns - I have no idea what this part is since you didn't go into much detail about it. Then either you submit a form or you send an AJAX request to the server to store "the timestamp" (what timestamp?) in the database. Break the whole thing down into discrete steps: scanning the QR code is one, validating with the dropdowns is another, scanning the second QR code is a third, and so on. Work on each step in turn.

Yeah, sure, it sounds all very possible. What do you need recommended? Sounds like you already know what you need to do.