I just completed my analysis of R-L21>Z253>A503. I collected the data for S7897 but the only tester was to be found S9897 only (father of A503). This pushed the limits too much and had to be removed. This is the 14th predictable haplogroup under Z253 which now covers 66 % of all Z253 testers. First is the source file for the analysis. It includes formulas for the signature match, the genetic distance from the signature and the prediction model using AcaStat. I found 50 testers confirmed to be A503 and the model predicted another 125 testers at Y67:

http://www.rcasey.net/DNA/Temp/S7897...20201108B.xlsx

Here are the input and output files for the SAPP charts:

http://www.rcasey.net/DNA/Temp/S7897..._20201108B.txt

http://www.rcasey.net/DNA/Temp/S7897_SAPP_Output_20201108B.html

http://www.rcasey.net/DNA/Temp/S7897..._20201108B.png