Also, being able to accurately measure spectral response would also allow one to accurately characterize something like a particular piece of blue cellophane or an inexpensive set of blue goggles as a suitable light filter, both of which (combined with the Mk-I eyeball) would be more accessible and convenient for a wider pool of users. This in in contrast to just hazily telling people, "well, you could *probably* use a piece of blue cellophane and it would probably be good enough to crudely tell you..."