#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<ll> vll;
typedef pair<ll, ll> pii;
//#define DEBUG

#ifdef DEBUG
const ll N = 1010;
#endif
#ifndef DEBUG
const ll N = 1001000;
#endif
pii a[N];
ll n;
bool chk(ll d)
{
	ll pt, l1, r1, l2, r2;
	pt = 0;
	l1 = l2 = -1E12;
	r1 = r2 = 1E12;
	for(ll i=0; i<n; i++)
	{
		ll dist = d * (a[i].first - pt);
		l1 -= dist; l2 -= dist;
		r1 += dist; r2 += dist;
		ll rx = -1E12, lx = 1E12;
		if (a[i].second >= l1 && a[i].second <= r1)
			rx = max(rx, r2), lx = min(lx, l2);
		if (a[i].second >= l2 && a[i].second <= r2)
			rx = max(rx, r1), lx = min(lx, l1);
		if(lx > rx) return 0;
		pt = a[i].first;
		l1 = a[i].second, r1 = a[i].second;
		l2 = lx, r2 = rx;
	}
	return 1;
}
int main()
{
	#ifndef DEBUG
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	#endif
	#ifdef DEBUG
	freopen("1.txt", "r", stdin);
	#endif
	ll z=  1;
	cin >> z;
	while(z--)
	{
		cin >> n;
		
		for(ll i=0; i<n; i++)
		{
			ll x, y;
			cin >> x >> y;
			a[i] = {x, y};
		}
		ll lb = 0, rb = 100000001;
		while(lb < rb)
		{
			ll mid = (lb+rb) / 2;
			if(chk(mid)) rb = mid;
			else lb = mid+1;
		}
		if(lb == 100000001) cout << -1 << '\n';
		else cout << lb << '\n';
	}
	return 0;
}