AviSynth and PAR

[Thar]

I would like to know, how does AviSynth handles various PARs? I am currently using AvsP (great tool by the way) and try to deal with 8:9 PAR material. While checking 720x480 --> 640x480 resize, included calculator shows me that target PAR would be 1:1 square pixels. Is AviSynth automatically converts PAR in the process? Or is it mistake on AvsP's part, and if yes, how can I manipulate PAR using AviSynth?

[GodofaGap]

There is no need for Avisynth to keep track of the PAR (it even can't) as it's purely a setting for a decoder in a player environment. You have to calculate the new PAR yourself when you resize (like you did now) and use that in the encoder.