Ahh thanks so much, that clears it up for me! Every description of double entry I'd seen so far seemed to have the notion of keeping a running balance for each

Ahh thanks so much, that clears it up for me! Every description of double entry I'd seen so far seemed to have the notion of keeping a running balance for each account (and then having a separate transaction for each one where they all sum to zero) as a central feature, so I thought avoiding that would make it no longer double-entry, and it always puzzled me why that was so crucial. Your comment made me see that wasn't actually the point!