This paper will discuss the precision of the Moderator Temperature Coefficient (MTC) estimate by noise analysis. Until now all attention went to the discussion of the bias of the MTC estimate that is due to the use of a small number of temperature sensors. However the discussion of the precision of the estimate was neglected. We will study the relation between the relative precision, the measurement time and the coherence. Based on this relation rules of thumb will be given in order to estimate the required measurement time for a specified precision and a given measurement setup. We will explain how a low coherence results in a large standard deviation. Next it will be shown that the standard deviation can be decreased by increasing the measurement time. The theoretical analysis will be verified by simulations in MATLAB and measurements at a Nuclear Power Plant in Belgium. From the measurements it will be seen that in practice we expect a coherence of 0.1 at a frequency lower than 0.1Hz. This results in a measurement time of more than 9 days if we want to achieve a standard deviation of 1%. A standard deviation of 5% can be achieved with a measurement time larger than 11h. This indicates that low coherences can result in unrealistic measurement times during which the reactor has to stay stationary.