The fixed and non-fixed veset, the onah beinonit (30 days), the veset ha-haflagot, dilug and sirug, the days of the month and the week, the veset ha-guf and the uprooting of a veset (Shulchan Aruch, Yoreh De'ah 189 — 34 se'ifim)
כָּל אִשָּׁה שֶׁאֵין לָהּ וֶסֶת קָבוּעַ — חוֹשֶׁשֶׁת לְיוֹם שְׁלֹשִׁים לִרְאִיָּתָהּ, שֶׁהִיא עוֹנָה בֵּינוֹנִית לִסְתָם נָשִׁים; וְאִם יֵשׁ לָהּ וֶסֶת קָבוּעַ לִזְמַן יָדוּעַ — חוֹשֶׁשֶׁת לַזְּמַן הַיָּדוּעַ.
Every woman who has no fixed veset is wary of the 30th day from her sighting, which is the onah beinonit (the average interval) of most women; and if she has a fixed veset at a known time, she is wary of that known time.
Shulchan Aruch, Yoreh De'ah 189:1LEVEL 01
Hebrew text of the 34 se'ifim with a fluent English translation. The onah beinonit (30 days), establishing a veset in 3 sightings, the veset ha-haflagot, dilug, the days of the month and week, the veset ha-guf and uprooting a veset, explained with practical cases (calendar, taharat ha-mishpacha app).
📖 StudyLEVEL 02
In-depth pilpul: the nature of the chashash veset (de-oraita or de-rabbanan, linked to siman 184), the logic of the chazakot (3 times to establish, 3 times to uproot), why the veset ha-haflagot requires 4 sightings, the combinatorics of haflagah / month / week / dilug / sirug (the Taz greatly developed), and isolating the cause in the veset ha-guf (הוברר הדבר).
📖 StudyLEVEL 03
Comparative tables (fixed / non-fixed, onah beinonit, haflagah / dilug / sirug, days of the month / week, veset ha-guf), golden rules, classic pitfalls (day / night, the first sighting that does not count in haflagah) and memorization of the 8 families covering the 34 se'ifim.
📖 StudyLEVEL 04
The shitah of the Tzemach Tzedek of Lubavitch and the Chabad mesorah on the rigorous tracking of vesatot, then the halacha lema'asse according to the Beit Yosef, the Rama, the Shach, the Taz, the Sidrei Tahara, the Chochmat Adam, the Aroch haShulchan and contemporary psak (Taharat haBayit, Shevet haLevi). The complexity of the calculation requires consulting a Rav.
📖 StudyA veset kavua (fixed cycle) is a cycle that has recurred regularly and that — according to the Shulchan Aruch (YD 189:2) — is established by three identical sightings (וביניהם ג׳ זמנים שוין), four sightings for the veset ha-haflagot. As long as it has not been uprooted three times, the woman is bound to it and must perform a בדיקה even if the onah passed without her sensing anything. A veset she-eino kavua (non-fixed cycle) has not reached this regularity: one is wary of it only once, and if it passes without her seeing, she is permitted. The real complexity of the calculation requires consulting a Rav.
The onah beinonit is the marker of the 30th day: every woman who has no fixed veset is wary of the 30th day from her sighting (חוששת ליום ל׳ לראייתה שהיא עונה בינונית לסתם נשים — YD 189:1), since it is the average interval of most women. The Shulchan Aruch (189:4) clarifies that this onah beinonit of 30 days has the status of a fixed veset: even if it passed without a בדיקה, one does not relax it as for a mere non-fixed cycle. In practice it is the marker day of most women today; but applying it requires a Rav.
A veset is established in several ways. The veset ha-haflagot rests on the interval between sightings (e.g. every 28 days). The dilug (shift) is an interval that lengthens regularly (30, 31, 32…). One also establishes a veset by the days of the month (the 1st of each month) or of the week, equal or not, with the sirug (skipping a month, where the 1st sighting counts). Finally the veset ha-guf is established by a bodily sign: yawning (פיהוק), sneezing, abdominal pain, chills, or — according to the Rama (189:23) — eating garlic, onion or pepper. Each type is established in 3 times and does not combine with another. In practice, consult your Rav.
The akirat veset is the extinction of a cycle. A fixed veset is uprooted only after three times in which the onah passes without her seeing (YD 189:14-16); as long as it has not been uprooted three times, she continues to be wary of it. If she returns to her former veset, it regains its force (חזר הוסת למקומו). A non-fixed veset, on the other hand, is uprooted from a single time without a sighting. The exact calculation — establishing, uprooting, returning, as well as the laws of the ketanah, the zekenah, the pregnant and the nursing woman (mesuleket damim) — is one of the most technical chapters of halacha: never rule alone on a real case, consult your Rav.