#include<bits/stdc++.h>
using namespace std;

#define int long long
const int N=1e6+100,INF=1e9;
#define gc getchar()
#define rd read()
inline int read(){
	int x=0,f=0; char c=gc;
	for(;c<'0'||c>'9';c=gc) f|=(c=='-');
	for(;c>='0'&&c<='9';c=gc) x=(x<<1)+(x<<3)+(c^48);
	return f?-x:x;
}

int n,t[N],x[N];

int chk(int v){
	int p=x[1],l=-INF,r=INF;
	for(int i=2,dt,l0,r0;i<=n;++i){
		dt=(t[i]-t[i-1])*v,l0=INF,r0=-INF;
		if(p-dt<=x[i]&&x[i]<=p+dt) l0=min(l0,l-dt),r0=max(r0,r+dt);
		if(l-dt<=x[i]&&x[i]<=r+dt) l0=min(l0,p-dt),r0=max(r0,p+dt);
		p=x[i],l=l0,r=r0;
	}
	return l<=r;
}

void solve(){
	n=rd; for(int i=1;i<=n;++i) t[i]=rd,x[i]=rd;
	
	int l=0,r=INF;
	while(l<r){
		int mid=l+r>>1;
		if(chk(mid)) r=mid;
		else l=mid+1;
	}
	printf("%lld\n", l==INF?-1:l);
}

signed main(){
	
	int T=rd;
	while(T--) solve();
	
	return 0;
}