Precision measurement of a period(s) of an embedded clock oscillator using a charge time measurement unit (CTMU) maintains a desired frequency accuracy of the embedded clock oscillator over a range of time, temperature and operating condition changes. The CTMU determines the free running frequency of the embedded clock oscillator and provides very accurate frequency (period) information for confirmation that a desired frequency, e.g., within 0.25 percent of the desired frequency, is running or an indication of how much and which direction to adjustment the frequency of the clock oscillator to maintain the frequency precision desired. Automatic frequency adjustment of the embedded clock oscillator may be implemented so as to maintain the desired precision frequency thereof. Temperature and voltage compensation profiles for maintaining the accuracy of the CTMU may be stored in a table, e.g., nonvolatile memory, for a further improvement in absolute frequency accuracy of the embedded clock oscillator.