In practice , however , the definition means that high-precision realizations of the second should compensate for the effects of the ambient temperature ( black-body radiation ) within which atomic clocks operate and extrapolate accordingly to the value of the second as defined above . In practice , however , the definition means that high-precision realizations of the second should compensate for the effects of the ambient temperature ( black-body radiation ) within which atomic clocks operate , and extrapolate accordingly to the value of the second at a temperature of absolute zero .