#include <bits/stdc++.h>

using namespace std;

using ll = long long;

const int maxn = 1e6 + 100;

ll n;
pair<ll, ll> vec[maxn];
set<pair<ll, ll>> all;
unordered_set<ll> all_pos;
ll V;

bool valid(ll i, ll j) {
    auto [t1, p1] = vec[i];
    auto [t2, p2] = vec[j];
    return abs(p1 - p2) <= abs(t1 - t2) * V;
}

void insert(ll pos) {
    auto [t, p] = vec[pos];
    // insert (p - tV, -p-tV)
    // ...
    auto x = p - t * V;
    auto y = -p - t * V;

    bool flag = true;
    auto rit = all.lower_bound({x, y});
    if (rit == all.end())
        flag = true;
    else {
        auto [tx, ty] = *rit;
        if (ty < y)
            flag = true;
        else
            flag = false;
    }
    if (flag) {
        auto it = rit;
        while (it != all.begin()) {
            auto pit = prev(it, 1);
            auto [tx, ty] = *pit;
            if (ty <= y)
                all.erase(pit);
            else
                break;
        }
        all.insert({x, y});
    }
}

vector<int> dp(maxn);

bool check() {
    all.clear();

    for (int i = 2; i < n; i++) {
        if (!valid(i - 1, i)) break;
        dp[i + 1] = true;
    }
    // check st = 2, i = 3?
    dp[2] = true;
    for (ll i = 3; i <= n; i++) {
        if (!valid(i - 2, i - 1)) {
            all.clear();
        }
        // cout << "addr2" << endl;
        if (dp[i - 1]) insert(i - 2);
        // j-1
        auto [qt, qp] = vec[i];
        auto qx = qp - qt * V;
        auto qy = -qp - qt * V;
        auto it = all.lower_bound({qx, qy});
        if (it != all.end()) {
            auto [tx, ty] = *it;
            if (ty >= qy) dp[i] = true;
        }
    }
    for (int temp = n; temp >= 1; temp--) {
        if (temp < n and !valid(temp, temp + 1)) break;
        if (dp[temp]) return true;
    }
    return false;
};

void solve() {
    cin >> n;
    for (ll i = 1; i <= n; i++) {
        cin >> vec[i].first >> vec[i].second;
    }
    all_pos.clear();
    for (ll i = 1; i <= n; i++) {
        all_pos.insert(vec[i].second);
    }
    if (all_pos.size() <= 2) {
        cout << 0 << '\n';
        return;
    }

    ll L = 1, R = 1e9 + 100;
    while (L < R) {
        ll mid = (L + R) / 2;
        V = mid;
        if (check())
            R = mid;
        else
            L = mid + 1;
    }
    if (L > 1e9) L = -1;
    cout << L << '\n';
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    ll t;
    cin >> t;
    while (t--) {
        solve();
    }

    return 0;
}