Heres my expert advice
In a measured value like "8.4126," the number value with the uncertainty is typically the last digit or the least significant digit. In this case, the number value with the uncertainty is "6." The uncertainty represents the potential variation or error associated with the measurement of the quantity.
So, for the measured value "8.4126," the uncertainty would be associated with the "6," and you might express it as ±0.0001 (if you consider it to be accurate to the thousandth's place) or ±0.1 (if you consider it to be accurate to the tenths place), depending on the level of precision and the measuring instrument used.