Is there a power supply or other device I could use to calibrate the Arduino? We use Arduinos in our testing fixtures at work and we need to be able to calibrate the test fixtures.
What's the Ardiuno used for? Timing measurements? Voltage measurements? Something else?
What I use for calibration is an external source to standardize the low and high extremes by writing those values to eeprom, I then use a range set of values for the low and high range and have those stored in eeprom. Using a formula derived by the map function, calculate the current value. I don't care if my values are a little low or high because what my arduino reads, I tell it what I want it to be. It doesn't matter if it's frequency, current or voltage, it all works the same.
If it is frequency or voltage out you can do something similar. If it is time, I would suggest a real time clock.
Whatever you do, to meet NIST standards will be hard to do. The best you can do is use standard tools that are NIST certified and match them with the arduino as close as you can.
I don't have the funds to have all of my test equipment NIST tested and certified but I have a Fluke 87 NIST certified and use it to verify my Fluke 789 Process Meter and an old Tektronix scope that I compare to a cheaper hand held scope and my old reliable Extech CMM-17 process calibrator. It's been a long time since I used decade boxes and wheatstone bridges. A certified decade box is just to cost prohibitive today for my work and I don't own a time standard but I have a cheap but effective frequency counter and function generator.
Don't beat yourself up trying to be exact. Accept a percent of error as acceptable. Even with some very expensive instrumentation devices for measuring process come with an acceptable or stated margin of error.
As in what Crossroads said, It would be good to know in what respect you talking about in calibrating the arduino.
I use 16 bit ADC's and DAC's and if the need be I could go higher for better resolution if the need be. I have developed a modular data logger and control system that communicates with with the modules with I2C using a Nano for the heart of it and sending the data either RS-232 or RS-485 back to the Data Logger software.
The Base-Master is 5x10 inches and less that 2 inches thick. I have current input and output modules, frequency input and output modules each 4 channel to a module and a 16 channel digital I/O and 16 channel relay driver module. I can run 12 modules from a single Bus-Master.
I'm currently designing an interface card for using the arduino Due, Mega and Uno plus Beaglebone and Raspberry Pi. The interface card supplies additionally two true RS-232 ports and signal level conversion. I2C is addressed by which slot the module is plugged into and is bank switched using an I2C hub.