Didn't really answer my question but to answer yours,"To validate the microwatt-meter design, a known resistor,
on measuring actual power consumption while the processor was doing things.
doing arithmetic with different variable types does not use the same power.
However the real answers are far more involved than you appear to intimate.
Integrate current with respect to time
That is a problem as the power consumption of microcontrollers and even the I2C bus depends on the supply voltage
Maybe my question was wrong. I was hoping for someone to help with finding a tool to measure the energy used in battery powered designs. For a good design it would be a priceless tool to help decide if method a or b is a better solution at each part.