I was taught split filter printing with blue and green filters. We started with a test strip that included part of the film rebate with the blue filter to determine maximum black. Then after exposing another sheet of paper for the maximum black time with the blue filter, another test strip with the green filter to determine the time for proper highlight values. I used that method successfully for some time, until another instructor taught the right use of variable contrast filters: expose for the highlights, and then adjust the shadows using higher or lower value filters. I believe my prints look just as good with proper variable contrast filters as they did with split filtering, and the exposure process is simpler to determine and carry out. I haven't used split filter printing since, except while burning in very high or low value areas of a print, then I use 0 and 5 filters.