[rthomas6]

My non-expert understanding for number 1 is that you would record the widget account in denominations of widgets, and separately, record the widget cost for that transaction. That's what you do in beancount anyway, which is what I use for home budgeting. Like this:

  2022-08-17 * "Purchase Widgets"
    Assets:Cash                  -100.00 USD
    Assets:Inventory:Widgets      10 WIDGET {10 USD}

Number 2 is just the reverse:

  2022-08-18 * "Sell Widget"
    Assets:Cash                   20 USD
    Assets:Inventory:Widgets      -1 WIDGET {20 USD}

Probably there's some other more professional way to do it, but this is what makes sense to me, and it's double entry.

[jdasdf]

Wouldn't that lead to a negative inventory value when the number of widgets is still positive?

[rthomas6]

No, because the inventory value is denominated in widgets, not USD.

What's important is that each transaction balances to zero. It doesn't have to balance across transactions.