This post is really for others' benefit as you believe you have successfully got an App but in another thread an APUGer was kind enough to give a link to his own site which simply requires that you input enlarger height or length measurement. The link is: home.centurytelnet/dwilder57/timeAdjust.html

Each time I experimented with the height I checked the exposure reading given by a probe on the same spot with what the site gave me and each time the figure was identical.