According to "This is the Torah" (Alfred J. Kolatch, 1988), there are 15 places in the Tanakh, with 10 in the Torah, where a dot or dots appear over one or more letters and even entire words. Such appearances of dots may have complex significance (e.g., see Two Dots, or Not Two Dots: אֶת is the Question., What Are Some Dots Between Brothers?!: Looking Both Ways, Concealing Overt Acts: Looking the Other Way, and Psalm 27: The Unique Case of Double Dots).
This source sheet considers a "simpler" case occurring in Num. 29:15 of ועשרוׄן עשׂרון:
(טו) וְעִשָּׂרוֹׄן֙ עִשָּׂר֔וֹן לַכֶּ֖בֶשׂ הָאֶחָ֑ד לְאַרְבָּעָ֥ה עָשָׂ֖ר כְּבָשִֽׂים׃
(15) and one-tenth for each of the fourteen lambs.
Why is there a dot over THIS vav (וׄ)?
The answer may be apparent by considering this to be a case of an outlier in a set of similar phrases or events. It is helpful to look at the immediate context of ועשרוׄן עשרון in Num. 28:11-29:17:
(יא) וּבְרָאשֵׁי֙ חׇדְשֵׁיכֶ֔ם תַּקְרִ֥יבוּ עֹלָ֖ה לַיקוק פָּרִ֨ים בְּנֵֽי־בָקָ֤ר שְׁנַ֙יִם֙ וְאַ֣יִל אֶחָ֔ד כְּבָשִׂ֧ים בְּנֵי־שָׁנָ֛ה שִׁבְעָ֖ה תְּמִימִֽם׃ (יב) וּשְׁלֹשָׁ֣ה עֶשְׂרֹנִ֗ים סֹ֤לֶת מִנְחָה֙ בְּלוּלָ֣ה בַשֶּׁ֔מֶן לַפָּ֖ר הָאֶחָ֑ד וּשְׁנֵ֣י עֶשְׂרֹנִ֗ים סֹ֤לֶת מִנְחָה֙ בְּלוּלָ֣ה בַשֶּׁ֔מֶן לָאַ֖יִל הָֽאֶחָֽד׃ (יג) וְעִשָּׂרֹ֣ן עִשָּׂר֗וֹן סֹ֤לֶת מִנְחָה֙ בְּלוּלָ֣ה בַשֶּׁ֔מֶן לַכֶּ֖בֶשׂ הָאֶחָ֑ד עֹלָה֙ רֵ֣יחַ נִיחֹ֔חַ אִשֶּׁ֖ה לַיקוק׃ (יד) וְנִסְכֵּיהֶ֗ם חֲצִ֣י הַהִין֩ יִהְיֶ֨ה לַפָּ֜ר וּשְׁלִישִׁ֧ת הַהִ֣ין לָאַ֗יִל וּרְבִיעִ֥ת הַהִ֛ין לַכֶּ֖בֶשׂ יָ֑יִן זֹ֣את עֹלַ֥ת חֹ֙דֶשׁ֙ בְּחׇדְשׁ֔וֹ לְחׇדְשֵׁ֖י הַשָּׁנָֽה׃ (טו) וּשְׂעִ֨יר עִזִּ֥ים אֶחָ֛ד לְחַטָּ֖את לַיקוק עַל־עֹלַ֧ת הַתָּמִ֛יד יֵעָשֶׂ֖ה וְנִסְכּֽוֹ׃ {ס} (טז) וּבַחֹ֣דֶשׁ הָרִאשׁ֗וֹן בְּאַרְבָּעָ֥ה עָשָׂ֛ר י֖וֹם לַחֹ֑דֶשׁ פֶּ֖סַח לַיקוק׃ (יז) וּבַחֲמִשָּׁ֨ה עָשָׂ֥ר י֛וֹם לַחֹ֥דֶשׁ הַזֶּ֖ה חָ֑ג שִׁבְעַ֣ת יָמִ֔ים מַצּ֖וֹת יֵאָכֵֽל׃ (יח) בַּיּ֥וֹם הָרִאשׁ֖וֹן מִקְרָא־קֹ֑דֶשׁ כׇּל־מְלֶ֥אכֶת עֲבֹדָ֖ה לֹ֥א תַעֲשֽׂוּ׃ (יט) וְהִקְרַבְתֶּ֨ם אִשֶּׁ֤ה עֹלָה֙ לַֽיקוק פָּרִ֧ים בְּנֵי־בָקָ֛ר שְׁנַ֖יִם וְאַ֣יִל אֶחָ֑ד וְשִׁבְעָ֤ה כְבָשִׂים֙ בְּנֵ֣י שָׁנָ֔ה תְּמִימִ֖ם יִהְי֥וּ לָכֶֽם׃ (כ) וּמִ֨נְחָתָ֔ם סֹ֖לֶת בְּלוּלָ֣ה בַשָּׁ֑מֶן שְׁלֹשָׁ֨ה עֶשְׂרֹנִ֜ים לַפָּ֗ר וּשְׁנֵ֧י עֶשְׂרֹנִ֛ים לָאַ֖יִל תַּעֲשֽׂוּ׃ (כא) עִשָּׂר֤וֹן עִשָּׂרוֹן֙ תַּעֲשֶׂ֔ה לַכֶּ֖בֶשׂ הָאֶחָ֑ד לְשִׁבְעַ֖ת הַכְּבָשִֽׂים׃ (כב) וּשְׂעִ֥יר חַטָּ֖את אֶחָ֑ד לְכַפֵּ֖ר עֲלֵיכֶֽם׃ (כג) מִלְּבַד֙ עֹלַ֣ת הַבֹּ֔קֶר אֲשֶׁ֖ר לְעֹלַ֣ת הַתָּמִ֑יד תַּעֲשׂ֖וּ אֶת־אֵֽלֶּה׃ (כד) כָּאֵ֜לֶּה תַּעֲשׂ֤וּ לַיּוֹם֙ שִׁבְעַ֣ת יָמִ֔ים לֶ֛חֶם אִשֵּׁ֥ה רֵֽיחַ־נִיחֹ֖חַ לַיקוק עַל־עוֹלַ֧ת הַתָּמִ֛יד יֵעָשֶׂ֖ה וְנִסְכּֽוֹ׃ (כה) וּבַיּוֹם֙ הַשְּׁבִיעִ֔י מִקְרָא־קֹ֖דֶשׁ יִהְיֶ֣ה לָכֶ֑ם כׇּל־מְלֶ֥אכֶת עֲבֹדָ֖ה לֹ֥א תַעֲשֽׂוּ׃ {ס} (כו) וּבְי֣וֹם הַבִּכּוּרִ֗ים בְּהַקְרִ֨יבְכֶ֜ם מִנְחָ֤ה חֲדָשָׁה֙ לַֽיקוק בְּשָׁבֻעֹ֖תֵיכֶ֑ם מִֽקְרָא־קֹ֙דֶשׁ֙ יִהְיֶ֣ה לָכֶ֔ם כׇּל־מְלֶ֥אכֶת עֲבֹדָ֖ה לֹ֥א תַעֲשֽׂוּ׃ (כז) וְהִקְרַבְתֶּ֨ם עוֹלָ֜ה לְרֵ֤יחַ נִיחֹ֙חַ֙ לַֽיקוק פָּרִ֧ים בְּנֵי־בָקָ֛ר שְׁנַ֖יִם אַ֣יִל אֶחָ֑ד שִׁבְעָ֥ה כְבָשִׂ֖ים בְּנֵ֥י שָׁנָֽה׃ (כח) וּמִ֨נְחָתָ֔ם סֹ֖לֶת בְּלוּלָ֣ה בַשָּׁ֑מֶן שְׁלֹשָׁ֤ה עֶשְׂרֹנִים֙ לַפָּ֣ר הָֽאֶחָ֔ד שְׁנֵי֙ עֶשְׂרֹנִ֔ים לָאַ֖יִל הָאֶחָֽד׃ (כט) עִשָּׂרוֹן֙ עִשָּׂר֔וֹן לַכֶּ֖בֶשׂ הָאֶחָ֑ד לְשִׁבְעַ֖ת הַכְּבָשִֽׂים׃ (ל) שְׂעִ֥יר עִזִּ֖ים אֶחָ֑ד לְכַפֵּ֖ר עֲלֵיכֶֽם׃ (לא) מִלְּבַ֞ד עֹלַ֧ת הַתָּמִ֛יד וּמִנְחָת֖וֹ תַּעֲשׂ֑וּ תְּמִימִ֥ם יִהְיוּ־לָכֶ֖ם וְנִסְכֵּיהֶֽם׃ {פ} (א) וּבַחֹ֨דֶשׁ הַשְּׁבִיעִ֜י בְּאֶחָ֣ד לַחֹ֗דֶשׁ מִֽקְרָא־קֹ֙דֶשׁ֙ יִהְיֶ֣ה לָכֶ֔ם כׇּל־מְלֶ֥אכֶת עֲבֹדָ֖ה לֹ֣א תַעֲשׂ֑וּ י֥וֹם תְּרוּעָ֖ה יִהְיֶ֥ה לָכֶֽם׃ (ב) וַעֲשִׂיתֶ֨ם עֹלָ֜ה לְרֵ֤יחַ נִיחֹ֙חַ֙ לַֽיקוק פַּ֧ר בֶּן־בָּקָ֛ר אֶחָ֖ד אַ֣יִל אֶחָ֑ד כְּבָשִׂ֧ים בְּנֵי־שָׁנָ֛ה שִׁבְעָ֖ה תְּמִימִֽם׃ (ג) וּמִ֨נְחָתָ֔ם סֹ֖לֶת בְּלוּלָ֣ה בַשָּׁ֑מֶן שְׁלֹשָׁ֤ה עֶשְׂרֹנִים֙ לַפָּ֔ר שְׁנֵ֥י עֶשְׂרֹנִ֖ים לָאָֽיִל׃ (ד) וְעִשָּׂר֣וֹן אֶחָ֔ד לַכֶּ֖בֶשׂ הָאֶחָ֑ד לְשִׁבְעַ֖ת הַכְּבָשִֽׂים׃ (ה) וּשְׂעִיר־עִזִּ֥ים אֶחָ֖ד חַטָּ֑את לְכַפֵּ֖ר עֲלֵיכֶֽם׃ (ו) מִלְּבַד֩ עֹלַ֨ת הַחֹ֜דֶשׁ וּמִנְחָתָ֗הּ וְעֹלַ֤ת הַתָּמִיד֙ וּמִנְחָתָ֔הּ וְנִסְכֵּיהֶ֖ם כְּמִשְׁפָּטָ֑ם לְרֵ֣יחַ נִיחֹ֔חַ אִשֶּׁ֖ה לַיקוק׃ {ס} (ז) וּבֶעָשׂוֹר֩ לַחֹ֨דֶשׁ הַשְּׁבִיעִ֜י הַזֶּ֗ה מִֽקְרָא־קֹ֙דֶשׁ֙ יִהְיֶ֣ה לָכֶ֔ם וְעִנִּיתֶ֖ם אֶת־נַפְשֹׁתֵיכֶ֑ם כׇּל־מְלָאכָ֖ה לֹ֥א תַעֲשֽׂוּ׃ (ח) וְהִקְרַבְתֶּ֨ם עֹלָ֤ה לַֽיקוק רֵ֣יחַ נִיחֹ֔חַ פַּ֧ר בֶּן־בָּקָ֛ר אֶחָ֖ד אַ֣יִל אֶחָ֑ד כְּבָשִׂ֤ים בְּנֵֽי־שָׁנָה֙ שִׁבְעָ֔ה תְּמִימִ֖ם יִהְי֥וּ לָכֶֽם׃ (ט) וּמִ֨נְחָתָ֔ם סֹ֖לֶת בְּלוּלָ֣ה בַשָּׁ֑מֶן שְׁלֹשָׁ֤ה עֶשְׂרֹנִים֙ לַפָּ֔ר שְׁנֵי֙ עֶשְׂרֹנִ֔ים לָאַ֖יִל הָאֶחָֽד׃ (י) עִשָּׂרוֹן֙ עִשָּׂר֔וֹן לַכֶּ֖בֶשׂ הָאֶחָ֑ד לְשִׁבְעַ֖ת הַכְּבָשִֽׂים׃ (יא) שְׂעִיר־עִזִּ֥ים אֶחָ֖ד חַטָּ֑את מִלְּבַ֞ד חַטַּ֤את הַכִּפֻּרִים֙ וְעֹלַ֣ת הַתָּמִ֔יד וּמִנְחָתָ֖הּ וְנִסְכֵּיהֶֽם׃ {ס} (יב) וּבַחֲמִשָּׁה֩ עָשָׂ֨ר י֜וֹם לַחֹ֣דֶשׁ הַשְּׁבִיעִ֗י מִֽקְרָא־קֹ֙דֶשׁ֙ יִהְיֶ֣ה לָכֶ֔ם כׇּל־מְלֶ֥אכֶת עֲבֹדָ֖ה לֹ֣א תַעֲשׂ֑וּ וְחַגֹּתֶ֥ם חַ֛ג לַיקוק שִׁבְעַ֥ת יָמִֽים׃ (יג) וְהִקְרַבְתֶּ֨ם עֹלָ֜ה אִשֵּׁ֨ה רֵ֤יחַ נִיחֹ֙חַ֙ לַֽיקוק פָּרִ֧ים בְּנֵי־בָקָ֛ר שְׁלֹשָׁ֥ה עָשָׂ֖ר אֵילִ֣ם שְׁנָ֑יִם כְּבָשִׂ֧ים בְּנֵֽי־שָׁנָ֛ה אַרְבָּעָ֥ה עָשָׂ֖ר תְּמִימִ֥ם יִהְיֽוּ׃ (יד) וּמִ֨נְחָתָ֔ם סֹ֖לֶת בְּלוּלָ֣ה בַשָּׁ֑מֶן שְׁלֹשָׁ֨ה עֶשְׂרֹנִ֜ים לַפָּ֣ר הָֽאֶחָ֗ד לִשְׁלֹשָׁ֤ה עָשָׂר֙ פָּרִ֔ים שְׁנֵ֤י עֶשְׂרֹנִים֙ לָאַ֣יִל הָֽאֶחָ֔ד לִשְׁנֵ֖י הָאֵילִֽם׃ (טו) וְעִשָּׂרוֹׄן֙ עִשָּׂר֔וֹן לַכֶּ֖בֶשׂ הָאֶחָ֑ד לְאַרְבָּעָ֥ה עָשָׂ֖ר כְּבָשִֽׂים׃ (טז) וּשְׂעִיר־עִזִּ֥ים אֶחָ֖ד חַטָּ֑את מִלְּבַד֙ עֹלַ֣ת הַתָּמִ֔יד מִנְחָתָ֖הּ וְנִסְכָּֽהּ׃ {ס} (יז) וּבַיּ֣וֹם הַשֵּׁנִ֗י פָּרִ֧ים בְּנֵי־בָקָ֛ר שְׁנֵ֥ים עָשָׂ֖ר אֵילִ֣ם שְׁנָ֑יִם כְּבָשִׂ֧ים בְּנֵי־שָׁנָ֛ה אַרְבָּעָ֥ה עָשָׂ֖ר תְּמִימִֽם׃
(11) On your new moons you shall present a burnt offering to יקוק: two bulls of the herd, one ram, and seven yearling lambs, without blemish. (12) As meal offering for each bull: three-tenths of a measure of choice flour with oil mixed in. As meal offering for each ram: two-tenths of a measure of choice flour with oil mixed in. (13) As meal offering for each lamb: a tenth of a measure of fine flour with oil mixed in. Such shall be the burnt offering of pleasing odor, an offering by fire to יקוק. (14) Their libations shall be: half a hin of wine for a bull, a third of a hin for a ram, and a quarter of a hin for a lamb. That shall be the monthly burnt offering for each new moon of the year. (15) And there shall be one goat as a sin offering to יקוק, to be offered in addition to the regular burnt offering and its libation. (16) In the first month, on the fourteenth day of the month, there shall be a passover sacrifice to יקוק, (17) and on the fifteenth day of that month a festival. Unleavened bread shall be eaten for seven days. (18) The first day shall be a sacred occasion: you shall not work at your occupations. (19) You shall present an offering by fire, a burnt offering, to יקוק: two bulls of the herd, one ram, and seven yearling lambs—see that they are without blemish. (20) The meal offering with them shall be of choice flour with oil mixed in: prepare three-tenths of a measure for a bull, two-tenths for a ram; (21) and for each of the seven lambs prepare one-tenth of a measure. (22) And there shall be one goat for a sin offering, to make expiation in your behalf. (23) You shall present these in addition to the morning portion of the regular burnt offering. (24) You shall offer the like daily for seven days as food, an offering by fire of pleasing odor to יקוק; they shall be offered, with their libations, in addition to the regular burnt offering. (25) And the seventh day shall be a sacred occasion for you: you shall not work at your occupations. (26) On the day of the first fruits, your Feast of Weeks, when you bring an offering of new grain to יקוק, you shall observe a sacred occasion: you shall not work at your occupations. (27) You shall present a burnt offering of pleasing odor to יקוק: two bulls of the herd, one ram, seven yearling lambs. (28) The meal offering with them shall be of choice flour with oil mixed in, three-tenths of a measure for a bull, two-tenths for a ram, (29) and one-tenth for each of the seven lambs. (30) And there shall be one goat for expiation in your behalf. (31) You shall present them—see that they are without blemish—with their libations, in addition to the regular burnt offering and its meal offering. (1) In the seventh month, on the first day of the month, you shall observe a sacred occasion: you shall not work at your occupations. You shall observe it as a day when the horn is sounded. (2) You shall present a burnt offering of pleasing odor to יקוק: one bull of the herd, one ram, and seven yearling lambs, without blemish. (3) The meal offering with them—choice flour with oil mixed in—shall be: three-tenths of a measure for a bull, two-tenths for a ram, (4) and one-tenth for each of the seven lambs. (5) And there shall be one goat for a sin offering, to make expiation in your behalf— (6) in addition to the burnt offering of the new moon with its meal offering and the regular burnt offering with its meal offering, each with its libation as prescribed, offerings by fire of pleasing odor to יקוק. (7) On the tenth day of the same seventh month you shall observe a sacred occasion when you shall practice self-denial. You shall do no work. (8) You shall present to יקוק a burnt offering of pleasing odor: one bull of the herd, one ram, seven yearling lambs; see that they are without blemish. (9) The meal offering with them—of choice flour with oil mixed in—shall be: three-tenths of a measure for a bull, two-tenths for the one ram, (10) one-tenth for each of the seven lambs. (11) And there shall be one goat for a sin offering, in addition to the sin offering of expiation and the regular burnt offering with its meal offering, each with its libation. (12) On the fifteenth day of the seventh month, you shall observe a sacred occasion: you shall not work at your occupations.—Seven days you shall observe a festival of יקוק.— (13) You shall present a burnt offering, an offering by fire of pleasing odor to יקוק: Thirteen bulls of the herd, two rams, fourteen yearling lambs; they shall be without blemish. (14) The meal offerings with them—of choice flour with oil mixed in—shall be: three-tenths of a measure for each of the thirteen bulls, two-tenths for each of the two rams, (15) and one-tenth for each of the fourteen lambs. (16) And there shall be one goat for a sin offering—in addition to the regular burnt offering, its meal offering and libation. (17) Second day: Twelve bulls of the herd, two rams, fourteen yearling lambs, without blemish;
Highlighted in bold above in the Torah text and English translation, six instances have the phrase עשרון עשרון, with some slight variation as well as a one being significantly different, though all with the same translated meaning: "one tenth":
(28:13) ועשרן עשרון; (28:21) עשרון עשרון ;(28:29) עשרון עשרון; (29:4) ועשרון אחד ;(29:10) עשרון עשרון; (29:15) ועשרוׄן עשׂרון.
Inspection of the letters in each of these six instances shows that each instance has exactly two ו, except the last one with the dot; the last instance has three ו.
Review of the text and translation reveals that each of the six instances concerns the measure (one tenth) of "choice flour with oil mixed in" for each of the seven yearling lambs in the burnt offering, except the last one. The last burnt offering involves one-tenth measure for each of the fourteen yearling lambs.
These differences suggest that the dot in ועשרוׄן עשׂרון points out its extra vav (וׄ) relative to the other five instances, with וׄ to signify double the number of yearling lambs in that burnt offering (14) relative to the seven yearling lambs in the other five burnt offerings.