It is crucial to monitor the deformation of dams for saving lives and properties, economy and the environment. Many critical observables have to be studied on the dam and the near vicinity. Mosul dam have been monitored according to many engineering standpoints since its construction more than two decades ago. In the last few years there was a debate on the safety of the dam. In this paper, the author made his own analysis on a subset of archived surveying measurements and field observations. Problems in data processing and probable causes of large errors in results are discussed. It shows that errors in measurement and analysis can cause fears and misleading concepts about safety of the dam. Full conclusions of the safety of the dam can only be obtained from a wide range of critical engineering limitations among which is the deformation monitoring.