I just had someone in my office, he explained to me that he has always had a hard time making sure the knot on his arm Tefillin touches the actual Tefillin box as is required.
I looked at it and realized right away that his Tefillin knot was on upside down.
That is a problem.
*Lesson* If you are having any problems with your Tefillin be sure to have a Certified Sofer/Scribe take a look at it.
Rabbi Kass was ordained by Rabbi Yisrael Meir Lau, former Ashkenazik Chief Rabbi of Israel. He is certified as a Sofer for both Kesivah and Hagoah by one of the leading experts in Safrus, Rabbi Avrohom Tzvi Vosner, Rav of the Vad Mishmeres Sta”m.