#include<bits/stdc++.h>
#pragma GCC optimize(3,"Ofast","inline")
// #pragma GCC target("avx2","sse2","fma")

using namespace std;

using ll = long long;

const int maxn = 1e6+100;

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

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

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

    auto 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});
        }
    };
    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;
        }
        //cout << "addr3" << endl;
        //cout << i << ' ' << dp[i] << endl;
    }
    // cout << V << endl;
    // exit(0);
    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; 
    // n = 1000000;
    for(ll i = 1 ; i <= n ; i ++) {
        cin >> vec[i].first >> vec[i].second;
        // vec[i].first = i;
        // vec[i].second = i;
    }
    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;
    }
    //cout << "addr1" << endl;

    ll L = 1, R = 5e8+100;
    while(L<R) {
        ll mid = (L+R)/2;
        if(check(mid)) R = mid;
        else L = mid + 1;

        //cout << "checking: " << L << ' ' << R << ' ' << check(mid) << endl;
    }
    if(L> 5e8) L = -1;
    cout << L << '\n';
}

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

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

    return 0;
}