In addition to the thorough manual examinations, it is very strongly recommended by gedolei Yisroel (Torah leaders) to computer check all Stam for textual errors. Although examiners do the best they can, humans can make mistakes that the computer can catch. However, the computer examination is not a substitute for the manual examination of missing, extra or substituted letters and words even though it has proven to be more accurate. Moreover, the computer cannot verify that the letters are written properly nor can it efficiently identify holes or separated or touching letters. This can only be accomplished through a meticulous manual examination by a qualified examiner.
The cost for the computer exam is minimal, and it is a one-time expense. If you have never had your tefillin or mezuzos computer checked, then it is advisable to do so next time you are having them examined. There are a number of reliable organizations and individuals who provide computer-checking services.
There are those who question the necessity for computer examination, claiming that just as the human eye is all that is required for checking produce, so too there is no need for more than a manual examination of Stam. However, there is an obvious difference between the two cases! The Torah forbids us to eat bugs. Therefore, we are obligated to check any food item that may be infested. Halachah only obligates us to check for bugs with the natural powers invested in us. If no bugs are visible to the naked eye then it is permissible to eat as the Torah considers it bug free. On the other hand the Torah requires us to don tefillin, and a missing letter, even if a human overlooks it, is still missing and makes the tefillin passul, invalid. The computer examination does not give us the power to see that which is not visible to the naked eye. It merely performs the same task as the human eye and transfers the reality to its brain. Unlike the human, the computer is not affected by distractions of any sort and it thereby performs the task of the human eye more efficiently. When an examiner checks Stam, his eyes also see a missing letter but this reality may not be transferred to his brain. When a missing letter is discovered by the computer, it becomes apparent to all.
Although previous generations relied only on manual examinations, today our power of concentration is weaker, and the sofer and examiner find it more difficult to direct their attention exclusively on their work. We also lack the fear of G-d of our ancestors, who trembled at the thought of making a mistake and constantly felt the great weight of responsibility upon them. Therefore, today computer checking is of great value.
This frightening story told by Reb Avrohom Veg, a Vizhnitzer chassid in Bnai Brak, illustrates the importance of computer examination: “From the day of my bar mitzvah around 40 years ago I’d been wearing tefillin with the most mehudar parshios, written by a well known sofer who had been used by the Chazon Ish! (Rabbi Avraham Yeshiya Karelitz, z”tl, a Torah giant who passed away in the 1950’s) During this time I had my tefillin checked nine times by expert examiners. I did my all to ensure that my tefillin were not only kosher but mehudar as well. When I found out that it was possible to have them computer-checked, I did so immediately, even though I was sure they would be okay. I was in total shock when I received a phone call that day from the Vaad Mishmeres STaM that I better put on a pair of tefillin right away, since they found that my tefillin were missing an entire word…”(Quoted in Speak of his Great Wonders by Rabbi Eli Teitelbaum [New York, 1992])