#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#define N 1000000
using namespace std;
const long long inf=(long long)(1e18);
const int INF=(int)(1e9);
int read()
{
	char c=0;
	int sum=0;
	while (c<'0'||c>'9') c=getchar();
	while ('0'<=c&&c<='9') sum=sum*10+c-'0',c=getchar();
	return sum;
}
struct reads
{
	int t,c;
};
reads st[N+1],delta[N+1];
struct rds
{
	long long a,b;
	int num;
	bool operator < (const rds &t)const
	{
		return a!=t.a?a<t.a:b<t.b;
	}
};
rds tong[N+1];
bool used[N+1];
int T,n,length;
bool check(int x)
{
	int l=1;
	long long minn;
	for (int i=1;i<=n;++i) used[i]=0;
	for (int i=1;i<=n-1;++i)
		if (abs(st[i+1].c-st[i].c)>1ll*(st[i+1].t-st[i].t)*x)
		{
			if (l==1)
			{
				for (int j=2;j<=i+1;++j) used[j]=1;
			}
			else
			{
				length=0;
				for (int j=max(l-1,1);j<=i+1;++j) tong[++length]=(rds){1ll*st[j].t*x-st[j].c,1ll*st[j].t*x+st[j].c,j};
				sort(tong+1,tong+length+1),minn=inf<<1;
				for (int j=1;j<=length;++j)
				{
					if (minn<=tong[j].b) used[tong[j].num]=1;
					if (used[tong[j].num+1]) minn=min(minn,tong[j].b);
				}
			}
			l=i+1;
		}
	if (l==1) return 1;
	for (int i=n;i>=1;--i)
	{
		if (i!=n&&abs(st[i+1].c-st[i].c)>1ll*(st[i+1].t-st[i].t)*x) return 0;
		if (used[i]) return 1;
	}
}
int main()
{
	int res;
	T=read();
	while (T--)
	{
		n=read(),res=-1;
		for (int i=1;i<=n;++i) st[i].t=read(),st[i].c=read();
		for (int i=log(INF)/log(2);i>=0;--i)
			if (res+(1<<i)<=INF&&!check(res+(1<<i)))
				res+=(1<<i);
		res++,printf("%d\n",res==INF+1?-1:res);
	}
	return 0;
}