The setting for TH requirement

i am sorry to trouble you ,but i have a quartus when i use the quartus10 and the timing analyzer is classsis timing analyzer .

first : when i click the assignment -> setting -> classic timing analyzer setting , then in the interface， i find the "th " , then i set the "th" 1ns ,it is ok, but i set it ''1.5ns" ,it show 15ns ,

then i use the .qsf ,and i use the TCL language which is "use set_global_assignment -name TH_REQUIREMENT "1.5 ns" " ， and in the " assignment setting " ,the TH_REQUIMENT show 1.5ns ?

then my quartus is why i cannot set the th "1.5ns" in the" assignment -> setting -> classic timing analyzer setting ,th" but i can set it in .qsf .

can you tell me which setting is write ?

thank you very much

dear