#include<iostream>
#include<cstring>
#include<vector>
#include<algorithm>
#include<set>
using namespace std;
using LL = long long;

int main(){

#ifdef LOCAL
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
#endif

    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);

    int T;
    cin >> T;
    while(T--){
        int n;
        cin >> n;
        vector<pair<int, int> > p(n);
        bool ok = true;
        for(int i = 0; i < n; i++){
            cin >> p[i].first >> p[i].second;
            if (i - 2 >= 0 and p[i].first == p[i - 2].first){
                ok = false;
            }
        }
        if (!ok){
            cout << -1 << '\n';
            continue;
        }

        auto check = [&](int mid){

            vector<pair<LL, LL> > q(n);
            for(int i = 0; i < n; i++){
                auto [t, x] = p[i];
                q[i] = {1LL * mid * t + x, 1LL * mid * t - x};
            }

            auto f = [&](int a, int b){
                return q[a].first <= q[b].first and q[a].second <= q[b].second;
            };

            set<pair<LL, LL> > s;

            auto insert = [&](pair<LL, LL> p){
                auto it = s.upper_bound(p);
                if (it != s.begin() and prev(s.begin())->second <= p.second) return;
                while(it != s.end() and it->second >= p.second){
                    it = s.erase(it);
                }
                s.insert(p);
            };

            bool ok = true;
            for(int i = 1; i < q.size(); i++){
                bool add = false, flag = true;
                if (ok) add = true;
                if (!f(i - 1, i)){
                    ok = false;
                    flag = false;
                }
                if (!add){
                    auto it = s.upper_bound(q[i]);
                    if (it != s.begin()){
                        --it;
                        if (it->second <= q[i].second){
                            add = true;
                        }
                    }
                }
                if (!flag) s.clear();
                if (add){
                    insert(q[i - 1]);
                }
                if (!ok and s.empty()) return false;
            }
            return true;
        };

        int l = 0, r = 1e9;
        while(l < r){
            int mid = (l + r) / 2;
            if (check(mid)) r = mid;
            else l = mid + 1;
        }
        cout << r << '\n';
    }

}