Why are the settings for vector chart contours different between the TZT9 and the TZTL12F? The shallow, safety and deep contours are like 3.0, 6.0, 9.0 for the TZT9 and 3.3, 6.6, 9.8 etc for the TZTL12F. Not a big difference, but enough so that the same map at the same location at the same scale is slightly different between the displays.