While OE gauges are not usually accurate, many have several modes, some may be more accurate than others. These mode may include tank average , instantaneous and on some cars the average for the last 15 minutes. Check your manual for specific information on you vehicle. If it didn't come with one the Toyota web site offers a downloadable PDF version.
Link to tracking fuel mileage.
https://ecomodder.com/blog/hypermili...l-consumption/