When putting together more than one sample of DNA in order to run the PCR gradient, what are the methods to group different samples of same species of DNA together besides having the Nano Drop reading measurements?
You mean Nanodrop 1000? You can go for Nanodrop 3000 or any other flourescent based measurement to get more precise DNA concentrations.
Do you want to mixture the DNA of different pure cultures with known amount of DNA? If that is the case the most precise method would be to do qPCR of every DNA alone to get the amount of target genes in the sample (not overall DNA amount).
But maybe that's like cracking a nut with a sledgehammer.