יורה דעה קפ״טYoreh De'ah 189

Se’if 1א׳

כָּל אִשָּׁה שֶׁאֵין לָהּ וֶסֶת קָבוּעַ, חוֹשֶׁשֶׁת לְיוֹם ל' לִרְאִיָּתָהּ, שֶׁהוּא עוֹנָה בֵּינוֹנִית לִסְתָם נָשִׁים, וְאִם יֵשׁ לָהּ וֶסֶת קָבוּעַ לִזְמַן יָדוּעַ מִכ' לְכ' אוֹ מִכ"ה לְכ"ה, חוֹשֶׁשֶׁת לַזְּמַן הַיָּדוּעַ.

Every woman who has no fixed veset (the fixed time at which a woman's period comes) is concerned for the thirtieth day from her sighting, which is the average onah (the interval, a day or a night, by which a woman's cycle is reckoned) for women in general. And if she has a fixed veset at a known time, from the twentieth to the twentieth or from the twenty-fifth to the twenty-fifth, she is concerned for the known time.

Se’if 2ב׳

כֵּיצַד קוֹבַעְתּוֹ, כְּגוֹן שֶׁתִּרְאֶה ד' פְּעָמִים, וּבֵינֵיהֶם ג' זְמַנִּים שָׁוִין, כְּגוֹן שֶׁרָאֲתָה הַיּוֹם, וּלְסוֹף כ' יוֹם פַּעַם אַחֶרֶת, וְעוֹד לְסוֹף עֶשְׂרִים יוֹם, וְעוֹד לְסוֹף כ' יוֹם, וְזֶה נִקְרָא וֶסֶת הַהַפְלָגוֹת. וּלְכָךְ צְרִיכָה ד' רְאִיּוֹת, שֶׁרְאִיָּה רִאשׁוֹנָה אֵינָהּ מִן הַמִּנְיָן, לְפִי שֶׁאֵינָהּ בְּהַפְלָגָה. וַאֲפִלּוּ קֹדֶם שֶׁקְּבַעְתּוֹ שָׁלֹשׁ פְּעָמִים חוֹשֶׁשֶׁת, שֶׁמִּיָּד אַחַר שֶׁרָאֲתָה פַּעַם אַחַת לְסוֹף כ' חוֹשֶׁשֶׁת מִכָּאן וְאֵילֵךְ כְּשֶׁיַּגִּיעַ כ', וְכֵן בִּרְאִיַּת הַיָּמִים שֶׁהִיא לְיָמִים יְדוּעִים לַחֹדֶשׁ, מִיָּד אַחַר שֶׁרָאֲתָה פַּעַם אַחַת לְיוֹם יָדוּעַ לַחֹדֶשׁ, כְּגוֹן כ"א אוֹ כ"ה בּוֹ, חוֹשֶׁשֶׁת לְפַעַם אַחֶרֶת לְזֶה הַיּוֹם, וַאֲסוּרָה לְשַׁמֵּשׁ כָּל אוֹתָהּ הָעוֹנָה. וְהוּא הַדִּין לִשְׁאָר מִינֵי וֶסֶת שֶׁצְּרִיכָה לָחוּשׁ לָהֶם כֵּן, חוּץ מִוֶּסֶת הַדִּלּוּג, וּכְמוֹ שֶׁיִּתְבָּאֵר בְּסִימָן זֶה. וְלֹא אָמְרוּ שֶׁצָּרִיךְ לְקָבִעָם ג' פְּעָמִים, אֶלָּא לְעִנְיַן עֲקִירָה, שֶׁכֵּיוָן שֶׁקּוֹבַעְתּוֹ בְּשָׁלֹשׁ פְּעָמִים אֵינוֹ נֶעֱקָר בְּפָחוֹת מִג' פְּעָמִים, שֶׁכָּל זְמַן שֶׁלֹּא עֲקַרְתּוֹ ג' פְּעָמִים צְרִיכָה לָחוּשׁ לוֹ. אֲבָל לֵאָסֵר, אֲפִלּוּ בְּפַעַם אַחַת חוֹשֶׁשֶׁת לוֹ פַּעַם שְׁנִיָּה. וּמִיהוּ, אַף עַל פִּי שֶׁחוֹשֶׁשֶׁת לוֹ, נֶעֱקַר בְּפַעַם אַחַת, אֲפִלּוּ קְבַעְתּוֹ ב' פְּעָמִים. שֶׁאִם רָאֲתָה ב' פְּעָמִים לְיוֹם יָדוּעַ, וּבַשְּׁלִישִׁית לֹא רָאֲתָה, אֵינָהּ חוֹשֶׁשֶׁת לוֹ עוֹד.

How does she fix it? Such as that she sees four times and between them are three equal times — such as that she saw today, and at the end of twenty days another time, and again at the end of twenty days, and again at the end of twenty days; and this is called the veset of intervals. And therefore she requires four sightings, since the first sighting is not of the count, because it is not by an interval. And even before she has fixed it three times she is concerned, for immediately after she has seen one time at the end of twenty she is concerned from here onwards when the twentieth arrives. And likewise as to the sighting of the days, which is on known days of the month: immediately after she has seen one time on a known day of the month, such as the twenty-first of it or the twenty-fifth of it, she is concerned for another time on this day, and she is forbidden to have intercourse all that onah. And the same law applies to the rest of the kinds of veset, that she must be concerned for them so, apart from the veset of skipping, and as will be explained in this siman. And they did not say that they must be fixed three times save with regard to uprooting: that since she fixes it in three times, it is not uprooted in less than three times, for so long as she has not uprooted it three times she must be concerned for it. But as to becoming forbidden, even by one time she is concerned for it a second time. However, even though she is concerned for it, it is uprooted in one time, even if she fixed it twice: for if she saw twice on a known day, and on the third she did not see, she is no longer concerned for it.

Se’if 3ג׳

אִם קָבְעָה וֶסֶת לְשָׁעוֹת וְלֹא לְיָמִים, אֵינָהּ חוֹשֶׁשֶׁת אֶלָּא שְׁעָתָהּ בִּלְבַד, וְהַוֶּסֶת הַזֶּה הוּא נֶעֱקָר בְּשָׁעָה אַחַת, וַאֲפִלּוּ בְּלֹא בְּדִיקָה.

If she has fixed a Veset for 'Shaot' (Times) and not 'Yamim' (Days) she is only 'Choshesh' (concerned) for the hour - and this Veset is uprooted in one hour even without a 'Bedika' (check /physical examination)