You could use a side by side question to add the validations.

And then use the JS below to create the constant sum experience.

Qualtrics.SurveyEngine.addOnReady(function () {
	const quest = this;
	const qc = quest.getQuestionContainer();
	const allCells = Array.from(qc.querySelectorAll(".AnswerCell"));
	const allCols = s];
	allCells
		.map((item) =>
			Array.from(item.classList).filter((a) => {
				if (a.includes("SBS") || a.includes("AnswerCell")) {
					return false;
				} else {
					return a;
				}
			})
		)
		.flatten()
		.forEach((a) => {
			if (allCols.indexOf(a) == -1) {
				allCols.push(a);
			}
		});

	const sumClass = allCols.pop();
	const selectors = allCols.map((a) => "." + a + " input");

	const allRows = Array.from(qc.querySelectorAll("tr.Choice"));

	allRows.forEach((row) => {
		const answerCell = row.querySelector("." + sumClass + " input");
		answerCell.disabled = true;
		answerCell.value = 0;

		selectors.forEach((col) => {
			const input = row.querySelector(col);
			input.type = "number";
			input.oninput = function () {
				updateSum(row);
			};
		});
	});

	const updateSum = function (row) {
		const allVals = selectors.map((item) => row.querySelector(item).value).map((item) => Number(item) || 0);

		const answerCell = row.querySelector("." + sumClass + " input");
		answerCell.value = allVals.reduce((a, b) => a + b);
	};
});

Demo: https://iima.au1.qualtrics.com/jfe/preview/previewId/00a1841e-33a5-49ae-a9c5-6934da853af4/SV_8HBDY4VRJnFn40J/BL_0Mt1Jw9T1Jby9eu?Q_SurveyVersionID=current

You can do this with two custom validation conditions, math expressions and piped values. Statement 1-Scale Point 2 should be equal to 100 minus all the other statements for scale point 2 AND Statement 1/Scale Point 3 should be equal to 100 minus all the other statements for scale point 3.

I can see where you’re going with this, but I just wanted to make sure if we’re on the same page.

Since the first column answers are being piped in (Their sum won’t necessarily be equal to 100), I want to make sure that the 2nd and 3rd column’s sum is in fact equal to 100. How can I go about applying validation for this?