Faced with this research, different authors have noted that the number line combined
with traditional subtraction rules is ineffective for making sense of subtractions involving
negative numbers.[14,19] Janvier [19] criticizes the ambiguity of this model, since numbers
are states (points on the line) or changes (arrows or movements along the line). He also
notes that many students who do well with the model pay more attention to the operation
than to the model itsel