IMHO this should be 1 to 1, see e.g. http://finance.yahoo.com/echarts?s=SAB#symbol=sab;range=1m;compare=sab.mx;indicator=volume;charttype=area;crosshair=on;ohlcvalues=0;logscale=off;source=undefined;
This is why SAB is a screaming buy at current distressed level. 60% loss when there is absolutely no change in the business value ;-)