Google Wallet, barcodes, self-service checkouts and feeling incompetent

I find it convenient to add gift1 and loyalty cards to Google Wallet on my Android phone. It keeps them in one quick-to-open place, often with self-updating gift card balances too. But one recurring bit of pain is that I often find it difficult to get self-service tills to scan barcodes shown from Google Wallet. And holding your phone at endless different angles in the hope that the barcode will scan, while someone is waiting behind you, is a good way to make you feel flustered and incompetent. Often even that doesn’t work, and you resort to scanning the barcode from somewhere else, like the retailer’s own app or a print-out, or you just give up. I’ve only really noticed this problem at the compact type of self-service till you’d often find at a Tesco Express, for example (and incidentally, a Tesco Clubcard is one of the things that gives me problems). Larger self-service tills like those at a Tesco superstore are usually no problem. I never really understood what the problem is – I…