Display's Kilowatts, £s, or $, CO2 emissions - shown by either hour, day, week, month or year also has a 24 hour clock display option. Memory function has the ability to store historical usage, CO2 emissions and cost comparisons by the hour, day, week, month and year. Real-time readings update every 4 seconds. Uses 4 AA batteries or can be used with the optional AC power adapters energy efficient; uses negligible electricity to operate. Estimated battery life is around 12-18 months.