#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
typedef long long ll;
constexpr int N = 1e6;
template <typename T> inline void read(T &x) {
    char ch; x = 0;
    while((ch = getchar()) <= 32);
    do {x = x * 10 + (ch & 15);} while((ch = getchar()) > 32);
}
template <typename T, typename ... _T>
inline void read(T &x, _T &...y) {read(x), read(y...);}
template <typename T> inline T abs(const T &x) {
    return x < 0 ? -x : x;
}
int n;
struct note {
    ll t, x;
} a[N + 3];
bool chk(ll v) {
    note lst;
    int vis = 0;
    for(int i = 2; i <= n; i++) {
        if(v * (a[i].t - a[i - 1].t) < abs(a[i].x - a[i - 1].x)) {
            if(!vis) {
                vis = 1;
            } else if(v * (a[i].t - lst.t) < abs(a[i].x - lst.x)) {
                return 0;
            }
            lst = a[i - 1];
        }
    }
    return 1;
}
int T;
int main() {
//    freopen("B.in", "r", stdin);
//    freopen("B.out", "w", stdout);
read(T);
while(T--){
    read(n);
    for(int i = 1; i <= n; i++) {
        read(a[i].t, a[i].x);
    }
    std::sort(a + 1, a + n + 1, [](note x, note y) {
        return x.t < y.t;
    });
    ll L = 0, R = 1'000'000'000;
    while(L <= R) {
        const ll mid = (L + R) >> 1;
        if(chk(mid)) R = mid - 1;
        else L = mid + 1;
    }
    printf("%lld\n", L<=1'000'000'000?L:-1);
}
    return 0;
}