OED online

[Jesse T Sheidlower]

> > This field force send in around 10,000 "slips" a year (as
> > against the 190,000 produced by the in-house lexicographers),
> > and would now seem to have a job for life.
>
> As I send in the electronic equivalent of about 12,000 slips a
> year myself, you may take that figure for external readers to be
> a gross underestimate (he's slipped a zero, I would guess).

For "year" read "month."

Jesse "Hiring for Life" Sheidlower
Oxford English Dictionary