#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define int long long
#define ii pair<int, int>
const int N = 2e6+5, M = 1e3+5, inf = 1e18, MOD = 1e9+7;
int n, m, x, y, res, test, k, sum1, cnt;
int t[N], c[N], l[N], r[N];

signed main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    cin >> test;
    while (test--) {
        cin >> n;
        for (int i = 1; i <= n; ++i) cin >> t[i] >> c[i];
        l[1] = r[n] = 0; res = 0;
        for (int i = 2; i <= n; ++i) {
            if (i > 2 && t[i] == t[i - 1] && t[i] == t[i - 2]) res = -1;
            if (abs(c[i] - c[i - 1]) % (t[i] - t[i - 1]) == 0) x = (int)abs(c[i] - c[i - 1]) / (int)(t[i] - t[i - 1]);
            else x = (int) abs(c[i] - c[i - 1]) / (int)(t[i] - t[i - 1]) + 1;
            l[i] = max(l[i - 1], x);
        }
        for (int i = n - 1; i > 0; --i) {
            if (abs(c[i] - c[i + 1]) % (t[i + 1] - t[i]) == 0) x = (int)abs(c[i] - c[i + 1]) / (int)(t[i + 1] - t[i]);
            else x = (int)abs(c[i] - c[i + 1]) / (int)(t[i + 1] - t[i]) + 1;
            r[i] = max(r[i + 1], x);
        }
//        for (int i = 1; i <= n; ++i) cout << l[i] << ' '; cout << endl;
//        for (int i = 1; i <= n; ++i) cout << r[i] << ' '; cout << endl;
        if (res == -1) cout << res << endl;
        else {
            res = (n == 1 ? 0 : inf);
            for (int i = 1; i < n; ++i) res = min(res, max(l[i], r[i + 1]));
            cout << res << endl;
        }
    }
}