Not sure if I can explain it well but you just need to find in-date sales (3 months or less) and provide the compare links of both the seller and buyer that show the transaction happening, you can also use SCM and MP.TF to find sales and for those you just gotta use the key prices for that day to convert the dollars into keys. At the end when you’re done going thru every in-date sale you make a range using the sales found, just have to make sure it makes sense and that you exclude sales if it seems valid to do so!