#include <bits/stdc++.h>
using namespace std;

bool Check(int N, vector<long long> &T, vector<long long> &C, long long V) {
	long long cl = 0;
	long long cr = (1LL << 30);

	// Simulation
	for (int i = 2; i <= N; i++) {
		bool flag = false;
		if (cl - V * T[i] <= C[i] && C[i] <= cr + V * T[i]) {
			flag = true;
		}

		// Second Choice
		if (T[i] - T[i - 1] == 0 || V * (T[i] - T[i - 1]) < abs(C[i] - C[i - 1])) {
			cl = 1LL * C[i - 1] + 1LL * V * T[i - 1];
			cr = 1LL * C[i - 1] - 1LL * V * T[i - 1];
			if (flag == false) return false;
		}
		if (flag == true) {
			cl = min(cl, 1LL * C[i] + 1LL * V * T[i]);
			cr = max(cr, 1LL * C[i] - 1LL * V * T[i]);
		}
	}
	return true;
}

int Solve(int N, vector<long long> T, vector<long long> C) {
	vector<pair<long long, long long>> Sorted;
	for (int i = 1; i <= N; i++) Sorted.push_back(make_pair(T[i], C[i]));
	sort(Sorted.begin(), Sorted.end());
	for (int i = 1; i <= N; i++) T[i] = Sorted[i - 1].first;
	for (int i = 1; i <= N; i++) C[i] = Sorted[i - 1].second;

	// Binary Search
	int cl = 0, cr = (1 << 30), cm, minx = (1 << 30);
	for (int i = 0; i < 35; i++) {
		cm = (cl + cr) / 2;
		bool ret = Check(N, T, C, cm);
		if (ret == true) { minx = min(minx, cm); cr = cm; }
		else { cl = cm; }
	}
	return (minx == (1 << 30) ? -1 : minx);
}

int main() {
	int T; scanf("%d", &T);
	for (int t = 1; t <= T; t++) {
		int N; scanf("%d", &N);
		vector<long long> T(N + 1, 0);
		vector<long long> C(N + 1, 0);
		for (int i = 1; i <= N; i++) scanf("%lld%lld", &T[i], &C[i]);
		printf("%d\n", Solve(N, T, C));
	}
	return 0;
}