As we continue to re-organize the lab at school (it never ends ) i re-discovered these hiding under a uv unit

there is a Macbeth TD504 it turns on , but since i don't have the directions i am not sure how to null it out to test

Macbeth TD901 this one does work with a refernce strip from my densitometer but is about .001 off.

this item has several channels to chose from but since we dont have the directions for this one i am unsure what, or which is used .

Both need cleaning.

This is for local pick up only as they are heavy (atlanta area) ; make a modest donation to the school and they are yours.