[Gretl-devel] First difference of a constant

Dear Gretl Team, Today I've found a very strange problem on Gretl. Please take a look at the following *hansl* code: <hansl> *open* hamilton.gdt *series* x = PC6IT *series* y = PZUNEW *series* z = EXRITL *series* teste = ((x[1989:01]/y[1989:01]) * z)/z * 100 *diff* teste *gnuplot* teste d_teste *--time-series --with-lines --output*=display </hansel> I think that mathematically the "teste" expression is a constant. So, the first difference of a constant variable is equal to zero. Am I missing something? Um abraço, *Henrique Coêlho de Andrade*