 An obvious visual difference between an original and a Watson Standard reboilered locomotive is usually a rectangular regulator cover, just to the rear of the chimney on the reboilered locomotive.In the case of the Class 16 and Class 16R locomotives, two even more obvious differences are the Watson cab and the absence of the Belpaire firebox hump between the cab and boiler on the reboilered locomotives.The Class 16 was intended for fast passenger trains in Transvaal, the Orange Free State and the upper sections of Natal where the gradients were not as severe.