Under the assets tab details of an asset, you will see a Readings tab.
Clicking on this tab displays the most recent meter reading recorded, on the asset, for every unit that asset has.
You will also see a floating + button which can be used to add a new meter reading on the asset.
When you click on the + button to add a new meter reading, you will have the option to select the meter reading unit and then add the reading to that unit.
The newly added reading will replace the last reading displayed for that unit after sync.
Till then, the last 2 readings will be visible