#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;

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

void insert(ll pos, ll V) {
    auto [t, p] = vec[pos];
    // insert (p - tV, -p-tV)
    // ...
    auto x = p - t * V;
    auto y = -p - t * V;
    while (all.size()) {
        auto it = all.lower_bound({x + 1, -3e18});
        if (it == all.begin()) break;
        auto [tx, ty] = *(--it);
        if (ty <= y) all.extract({tx, ty});
    }

    bool flag = true;
    if (all.size()) {
        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) all.insert({x, y});
}

bool check(ll V) {
    static bool dp[maxn];
    std::fill(dp, dp + n + 1, 0);
    all.clear();

    // check st = 2, i = 3?
    dp[2] = true;
    for (ll i = 3; i <= n; i++) {
        if (!valid(i - 2, i - 1, V)) {
            all = {};
        }
        if (dp[i - 1]) insert(i - 2, V);
        // 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;
        }
    }
    return dp[n];
};

void solve() {
    cin >> n;
    for (ll i = 1; i <= n; i++) {
        cin >> vec[i].first >> vec[i].second;
    }
    unordered_set<ll> all_pos;
    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;
        if (check(mid))
            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;
}