function calculation()
{	
	if(f1.lgth.selectedIndex==0 && f1.size.selectedIndex==0)
	{
		alert("Select Length & Size");
	}
	if(f1.lgth.selectedIndex==1 && f1.size.selectedIndex==1)
	{
		window.location="rainwater-calculator.htm#10x140";
	}
	if(f1.lgth.selectedIndex==1 && f1.size.selectedIndex==2)
	{
		window.location="rainwater-calculator.htm#10x180";
	}
	if(f1.lgth.selectedIndex==1 && f1.size.selectedIndex==3)
	{
		window.location="rainwater-calculator.htm#10x250";
	}
	if(f1.lgth.selectedIndex==2 && f1.size.selectedIndex==1)
	{
		window.location="rainwater-calculator.htm#20x140";
	}
	if(f1.lgth.selectedIndex==2 && f1.size.selectedIndex==2)
	{
		window.location="rainwater-calculator.htm#20x180";
	}
	if(f1.lgth.selectedIndex==2 && f1.size.selectedIndex==3)
	{
		window.location="rainwater-calculator.htm#20x250";
	}
	if(f1.lgth.selectedIndex==3 && f1.size.selectedIndex==1)
	{
		window.location="rainwater-calculator.htm#30x140";
	}
	if(f1.lgth.selectedIndex==3 && f1.size.selectedIndex==2)
	{
		window.location="rainwater-calculator.htm#30x180";
	}
	if(f1.lgth.selectedIndex==3 && f1.size.selectedIndex==3)
	{
		window.location="rainwater-calculator.htm#30x250";
	}
	if(f1.lgth.selectedIndex==4 && f1.size.selectedIndex==1)
	{
		window.location="rainwater-calculator.htm#40x140";
	}
	if(f1.lgth.selectedIndex==4 && f1.size.selectedIndex==2)
	{
		window.location="rainwater-calculator.htm#40x180";
	}
	if(f1.lgth.selectedIndex==4 && f1.size.selectedIndex==3)
	{
		window.location="rainwater-calculator.htm#40x250";
	}
	if(f1.lgth.selectedIndex==5 && f1.size.selectedIndex==1)
	{
		window.location="rainwater-calculator.htm#50x140";
	}
	if(f1.lgth.selectedIndex==5 && f1.size.selectedIndex==2)
	{
		window.location="rainwater-calculator.htm#50x180";
	}
	if(f1.lgth.selectedIndex==5 && f1.size.selectedIndex==3)
	{
		window.location="rainwater-calculator.htm#50x250";
	}
	if(f1.lgth.selectedIndex==6 && f1.size.selectedIndex==1)
	{
		window.location="rainwater-calculator.htm#60x140";
	}
	if(f1.lgth.selectedIndex==6 && f1.size.selectedIndex==2)
	{
		window.location="rainwater-calculator.htm#60x180";
	}
	if(f1.lgth.selectedIndex==6 && f1.size.selectedIndex==3)
	{
		window.location="rainwater-calculator.htm#60x250";
	}
	if(f1.lgth.selectedIndex==7 && f1.size.selectedIndex==1)
	{
		window.location="rainwater-calculator.htm#70x140";
	}
	if(f1.lgth.selectedIndex==7 && f1.size.selectedIndex==2)
	{
		window.location="rainwater-calculator.htm#70x180";
	}
	if(f1.lgth.selectedIndex==7 && f1.size.selectedIndex==3)
	{
		window.location="rainwater-calculator.htm#70x250";
	}
	if(f1.lgth.selectedIndex==8 && f1.size.selectedIndex==1)
	{
		window.location="rainwater-calculator.htm#80x140";
	}
	if(f1.lgth.selectedIndex==8 && f1.size.selectedIndex==2)
	{
		window.location="rainwater-calculator.htm#80x180";
	}
	if(f1.lgth.selectedIndex==8 && f1.size.selectedIndex==3)
	{
		window.location="rainwater-calculator.htm#80x250";
	}
	if(f1.lgth.selectedIndex==9 && f1.size.selectedIndex==1)
	{
		window.location="rainwater-calculator.htm#90x140";
	}
	if(f1.lgth.selectedIndex==9 && f1.size.selectedIndex==2)
	{
		window.location="rainwater-calculator.htm#90x180";
	}
	if(f1.lgth.selectedIndex==9 && f1.size.selectedIndex==3)
	{
		window.location="rainwater-calculator.htm#90x250";
	}
	if(f1.lgth.selectedIndex==10 && f1.size.selectedIndex==1)
	{
		window.location="rainwater-calculator.htm#100x140";
	}
	if(f1.lgth.selectedIndex==10 && f1.size.selectedIndex==2)
	{
		window.location="rainwater-calculator.htm#100x180";
	}
	if(f1.lgth.selectedIndex==10 && f1.size.selectedIndex==3)
	{
		window.location="rainwater-calculator.htm#100x250";
	}

}