#include<bits/stdc++.h>
#define int long long
using namespace std;
int read()
{
	int x = 0, f = 1;
	char c = getchar();
	while(c != EOF and !isdigit(c))
	{
		if(c == '-')f = -1;
		c = getchar();
	}
	while(isdigit(c))
	{
		x = x * 10 + c - '0';
		c = getchar();
	}
	return x * f;
}
struct node{
	int t, c;
}a[1000010];
bool cmp(node x, node y)
{
	if(x.t == y.t)return x.c < y.c;
	return x.t < y.t;
}
int n;
bool checks()
{
	for(int i = 1;i + 2 <= n;i ++)if(a[i].t == a[i+1].t and a[i+1].t == a[i+2].t)return true;
	return false;
}
bool check(int mid)
{
	if(n <= 2)return true;
	int p = 1, q = -1, now = 1;
	if(a[1].t == a[2].t)
	{
		now = p = 2;
		q = 1;
	}
	for(int i = 2;i <= n;i ++)
	{
		if(a[i].t == a[i - 1].t)continue;
		//cout<<p<<' '<<q<<' '<<now<<endl;
		if(i + 1 <= n)
		{
			if(a[i].t == a[i + 1].t)
			{
				if(abs(a[i].c - a[now].c) > (a[i].t - a[now].t) * mid)
				{
					if(q != -1)
					{
						if((abs(a[i].c - a[p].c) > (a[i].t - a[p].t) * mid or abs(a[i+1].c - a[q].c) > (a[i+1].t - a[q].t) * mid))
						{
							//cout<<"cant\n";
							if((abs(a[i+1].c - a[p].c) > (a[i+1].t - a[p].t) * mid or abs(a[i].c - a[q].c) > (a[i].t - a[q].t) * mid))
							{
								return false;
							}
							p = i + 1;
							q = i;
							now = i + 1;
							continue;
						}
					}
					else{
						if(abs(a[i].c - a[p].c) > (a[i].t - a[p].t) * mid or (abs(a[i+1].c - a[p].c) > (a[i+1].t - a[p].t) * mid))
						{
							return false;
						}
						p = i + 1;
						q = i;
						now = i + 1;
						continue;
					}
				}
				//cout<<i<<"?"<<endl;
				p = i + 1;
				q = i;
				now = i + 1;
				continue;
			}
		}
		if(abs(a[i].c - a[now].c) <= (a[i].t - a[now].t) * mid)
		{
			now = i;
			continue;
		}
		if(q == -1 or abs(a[i].c - a[p].c) <= (a[i].t - a[p].t) * mid or abs(a[i].c - a[q].c) <= (a[i].t - a[q].t) * mid)
		{
			//cout<<"???\n";
			q = now;
			now = i;
			p = i;
			continue;
		}
		return false;
	}
	return true;
}
signed main()
{
	int T = read();
	while(T --)
	{
		n = read();
		for(int i = 1;i <= n;i ++)
		{
			a[i].t = read();
			a[i].c = read();
		}
		sort(a + 1, a + n + 1, cmp);
		if(checks())
		{
			cout<<-1<<'\n';
			continue;
		}
		int l = 0, r = 1e9, ans = -1;
		//check(2);
		while(l <= r)
		{
			int mid = l + r >> 1ll;
			//cout<<mid<<endl;
			if(check(mid))
			{
				r = mid - 1;
				ans = mid;
			}
			else l = mid + 1;
		}
		cout<<ans<<'\n';
	}
	return 0;
}