Good Morning Zelda, I wish I could answer your question but since I'm not familiar with AT2 readings will defer to someone who is.
Hope you are doing well...good to see Walter giving some nice numbers last night. I would not decrease on TR with those numbers - but I do not use AT2; I thought 68 was equivalent to 50 on human meter - and for us we wait until we've hit three drops below 50 before Luci earns a reduction as she hasn't held reductions well in the past; once below 40 will earn her a reduction (or as in the case of this week, her mama is too sick to properly monitor, so I reduced her dose to keep her safe)...