The object of this code is to let you look at your mistakes on your own and learn from them.
sp Spelling e.g. Friends not frinds.
gr Grammar e.g. Lots of money not many money.
pr Preposition eg. I live in London not I live at London.
pu Punctuation e.g. I like milk not i like milk.
vt Verb tense e.g. I went to Spain in 1995 not I have gone to Spain in 1995.
wo Word order e.g. I like dancing very much not I like very much dancing.
ww Wrong word e.g. I missed the bus not I lost the bus.
mw Missing word e.g. I saw a bird not I saw bird.
r Repetition i.e. saying the same again and again and again etc.