Does the metric requirement apply to just the diagram, or to the flight log as well?

The requirement to report metric units applies to diagrams as well as the Flight Log. The diagram IS part of the flight log. Where appropriate (e.g.; dimensions, temperature) Science Olympiad participants should convert units into the Metric equivalent. In cases where data is reported by a measuring device in a non-metric format and those results are not traditional, or easily converted, (i.e., torque) then it is acceptable that the results use the units from the device.