Why does McMahon say that Carlyle's arithmetic was essentially sound?

McMahon argues that Carlyle's arithmetic was essentially sound because it adhered to fundamental mathematical principles, despite any unconventional methods or interpretations he employed. Carlyle's approach demonstrated a consistent logic and coherence that, when examined closely, aligned with established arithmetic practices. This indicates that his calculations, while perhaps unconventional, were based on a solid understanding of mathematical concepts. Thus, McMahon acknowledges the validity of Carlyle's arithmetic within its own framework.