The idea of strip model is further developed and supplemented by the list of necessary and sufficient conditions to explain why the frequency shift changes its sign for the opposite one. Actually, a load (either point or distributed) is linked to the QCM surface through some elastic bonds rather than rigin ones. Because of this, the frequnecy shift may take on the values opposite in signs. It is demonstrated that the strip model is so general that it fits well with its points to the experimental curves recorded for different QCM samples. To predict the sign of the frequency shift, we introduce an elastic bond between the nanoobject and QCM surface, and describe a semi-analytical solution which explains why the sign of the frequnecy shift changes.