How Accurate Are Digital Thermometers?

I wanted to know my temperature, so I would know when I have a fever.  I was also curious how my temperature compares to "normal" people.  

But first, I had to figure out how accurate my digital thermometer is.

Accuracy is how close a measurement is to the true value; precision is how much variability there is in repeated measurements.  The thermometer says it is accurate to within +/- 0.2 F, but I have no way to test that because I have no other measurement of my temperature to compare it with.  I can test the precision by taking multiple readings in a row.  This usually yields the same number, indicating that the precision is very good (i.e. low variability).  However, sometimes, depending on how I hold the thermometer, the readings can vary by as much as 0.4.

What is my normal temperature?  

To test this, I took my temperature over 10 days in April, 2024.  I took 48 readings, a total of 3-4 for each hour of the day.  For each reading I lay down for a minute and then put the thermometer in my mouth, as far back under the tongue as possible.  Each reading took 90-120 seconds, so this effort included more than an hour of total time spent taking my temperature.

My average temperature is 97.4, almost a full degree less than the widely-quoted population average of 98.2.  Standard deviation is 0.6 degrees, so 68% of the time my temperature is between 96.8 and 98.  This variability include any precision variability in the thermometer.

My temperature usually reaches a minimum in the morning, rises to a maximum is in late afternoon / early evening, and then begins to fall before bedtime.  My highest temperatures were recorded after exercise, doing chores, eating a warm/fatty dinner, and lying in the sun.  Minimum temperatures were recorded lying in bed, after exercise, and after breakfast.