#include<bits/stdc++.h>
#define int long long
using namespace std;
inline int read()
{
	int n=0,f=1,ch=getchar();
	while(ch<'0'||ch>'9')
	{
		if(ch=='-')f=-1;
		ch=getchar();
	}
	while(ch>='0'&&ch<='9')
	{
		n=n*10+ch-'0';
		ch=getchar();
	}
	return n*f;
}
int t[1000005],c[1000005];
int x1[1000005],x2[1000005],pos[1000005];
bool bi(int x,int y)
{
	if(x1[x]!=x1[y])return x1[x]<x1[y];
	return x2[x]<x2[y];
}
signed main()
{
	int T,n;
	T=read();
	for(int greg=1;greg<=T;greg++)
	{
		n=read();
		for(int i=1;i<=n;i++)
		{
			t[i]=read();
			c[i]=read();
		}
		int l=0,r=1000000000,mid;
		while(l<=r)
		{
			mid=((l+r)>>1);
			for(int i=1;i<=n;i++)
			{
				x1[i]=t[i]*mid+c[i];
				x2[i]=t[i]*mid-c[i];
				pos[i]=i;
			}
			sort(pos+1,pos+n+1,bi);
			int nl=0;
			bool flag=true;
			for(int i=2;i<=n;i++)
			{
				//if(mid==2)printf("%lld %lld\n",i,nl);
				if(x2[pos[i-1]]<=x2[pos[i]])
				{
					
				}
				else
				{
					if(nl==0||x2[pos[nl]]<=x2[pos[i]])nl=i-1;
					else
					{
						flag=false;
						break;
					}
				}
			}
			if(flag)r=mid-1;
			else l=mid+1;
		}
		if(l<=1000000000)printf("%lld\n",l);
		else printf("-1\n");
	}
	return 0;
}