LM4040D20 - 1% 2.048V Precision Voltage Reference
A voltage reference is an electronic device that produces a fixed (constant) voltage irrespective of the loading on the device, power supply variations, temperature changes, and the passage of time. Voltage references are used in power supply voltage regulators, analog-to-digital converters and digital-to-analog converters, and myriad other measurement and control systems.
Wide Operating Current Range…45 μA Typ to 15 mA
It's great for use with an Arduino getting extremelly correct values from the ADC.