Beethoven asks his friend Zmeskall to postpone his visit, as he is busy doing "important quartet corrections" which cannot be put off, "because they will be sent to be engraved the day after tomorrow". The handwriting and tone of address allow us to suppose it was written early on (according to the BGA). The quartets have therefore been identified as being op. 18. Beethoven had already sold the quartets to Mollo in autumn 1800, who published them in two volumes in June and October 1801. According to the BGA the letter was therefore written just before the first volume appeared, that is before June 1801.
