Troubleshooting Custom Cost-by-Customer Dashboard Showing Incorrect Units and Values

I'm trying to do a cost-by-customer dashboard, but it's not quite working the way I want. I received these instructions:

You can define a custom metric for cost (e.g. SELECT SUM(cost) FROM MODEL), then add it to a dashboard as a line chart. From there, you can group by any dimension on your traces/spans. So if you're tagging each trace/span with a customer identifier, you can group by that dimension and get a graph that breaks down LLM cost by customer.

But the chart looks wrong - it's not displaying in dollars and cents, and I can't tell if the amounts are in the right units, or if the amounts themselves are correct. Alyx seems to be down, or I would just ask there. Is there a step I'm missing?