import pandas as pd
daily = pd.DataFrame({"litres": [18., 22.], "hours": [3., 4.]}, index=["Mon", "Tue"])
daily["rate"] = daily["litres"] / daily["hours"]
assert daily.index.is_unique
assert daily.loc["Mon", "rate"] == 6.
assert daily.loc["Tue", "rate"] == 5.5
print("Mon 6.0 L/hour; Tue 5.5 L/hour")