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Comment by jtbayly | Hacker News Reader

That’s not the right comparison. What you want to compare is how long it takes at a staffed queue vs an unstaffed one once you get to the front of the line (for the same purchase).

Things might be faster now with the unmanned ones, but the contention is that that’s only because they opened more checkout terminals. Granted, they wouldnt have done that with staffed ones because of the increased expense, but let’s not get confused about the real cause.

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This seems like a faulty comparison. Space for registers is naturally limited. A single traditional register is replaced by 3 self-checkouts at my local grocery stores. Usually they opt for 6x self checkout replacing two traditional registers, manned by a single employee who can help with problems. In these cases it's not a question of staffing, but of space and the increase in space efficiency.

As always it depends on what you want to measure. Comparing total checkout time including queuing though for 'speed (items/s)' is going to naturally favor the self-checkout because the choice between normal and self checkout is heavily weighted by the number of items a particular person has. Anecdotally I've never seen anyone go through self checkout with a full cart but see it all the time with the normal registers. Additionally there's rarely the same number of traditional registers actually staffed compared to the number of self checkouts.

I agree. I would say that a better measure than items/s would be customers/hr (closer to throughput rather than speed) averaged across an entire store with and without self-checkouts. As you said, the optimal setup will depend heavily on the mix of customer types ("express" vs. full cart) a particular store gets. There's probably a good ratio for most stores between the two and I think that's what they're all converging on now.

Space comes with a price too. If you ignore all costs, a traditional checkout that is read when you walk up is probably faster most of the time vs an available self-checkout.

Agreed that space is a part of the comparison, but what I've seen is that although they put 3 checkouts in the y-axis space of a single staffed lane, they end up having to use up almost 3 times as much space in the x-axis to allow people to pass each other, which simply isn't necessary to allow in a staffed lane. So I don't believe the amount of space is that different.

No, there really is a huge difference. It's more like 1.5 times the y-axis space in your example, they could get 6 self service checkouts in the space of 2 staffed ones:

    >|1|   |2|   <    >|1|      |4|<
     | |   | |         |2|      |5|
     | |   | |         |3|      |6|

Or similar. What does slow things down is elderly or people apprehensive of technology, and tourists or others encountering them for the first time...

>What you want to compare is how long it takes at a staffed queue vs an unstaffed one once you get to the front of the line (for the same purchase).

Maybe if you're selling a checkout system. Personally I care how fast I can go from "got things" to "left building". (or maybe more accurately: left home -> returned home, but that has a lot more variables)

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