Ibn Ezra on Leviticus 23:15

לולי הקבלה היה נראה כי ספירת הימים כשנות היובל והמכחישים אמרו כי טעם תמימות שלא תעלה במספר השבת הראשונה שיחל ממחרת׳‎: If it were not for tradition¹⁶²That requires us to count the days between the waving of the omer and Shavu’ot. it would have appeared that the counting of the days is similar to the counting of the years¹⁶³Hebrew, ki-shenot. Some editions read bi-shenot. According to this reading, “the counting of days only applies in the days of the Jubilee.” In other words, the omer is not counted when the Jubilee is not observed. of the Jubilee.¹⁶⁴Forty-nine years (seven weeks of years) are counted and the 50th year declared as the year of Jubilee. Similarly, seven weeks would be counted from the offering of the omer and the 50th day declared as the festival of Shavu’ot. Those who deny the Rabbinic tradition say that the meaning of complete is that the first Sabbath from the morrow on which the count begins is not to be considered in the count.¹⁶⁵In other words, the Sabbath preceding the day on which the omer is waved is not to be considered in the count.