I was amazed that in the same article he used the word "sum" with complete abandon (division sum, subtraction sum). If he advocates correct terminology from the start, then he ought not to use sum to mean anything but the result of addition.
I was also surprised to find that he regarded square centimetre as equivalent to centimetre squared and suggested one could just choose between them.
However: two centimetres squared equals four square centimetres, three centimetres squared equals nine square centimetres . . .
FRANCES ASHWORTH Mathematics adviser Dorset