This article is an excerpt from our Sefer
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Blew a Teruah instead of a Shevarim or vice versa: In all cases that one was supposed to blow a Teruah or Shevarim and instead he blew a Shevarim or Teruah [i.e. one blew a Shevarim inתר”ת instead of a Teruah, or a Teruah in תש”ת instead of a Shevarim] he must start again from the Tekiah of that particular set. [Each of the three groupings in תשר”ת/תש”ת/תר”ת is considered a set for a total of 9 sets] This applies even if one only began the wrong blow, and then remembered right away.
If in תשר”ת one began blowing the Teruah before blowing the Shevarim: If one began blowing the Teruah prior to finishing blowing the 3 blows of the Shevarim, then if it was all done in one breath he does not need to re-blow the Tekiah of that set. Rather he is to simply reblow the Shevarim-Teruah. If however one took a breath in between the Shevarim and Teruah, or began blowing a Teruah before even beginning the Shevarim, he must start again from the Tekiah of that particular set.
Blew an extra set of Teruah or Shevarim: In all cases that one is supposed to blow a Shevarim or Teruah and he blew a second set. Then if the first set was Halachically valid he must repeat from the first Tekiah of that set, if he took a breath between the two sets. This applies even if he did not complete the second set, such as he only blew one Shevarim or one Terumatin. If, however, one did not take a breath in between the two sets, or if the previous set was not Halachically valid then he may continue with the last Tekiah of that set.