Elusive Coordinates

Exploration Stage: Hidden Row
From: Martha
Description: You remember being in a mysticism lovers society called the Secret League? The spirits say that you used to debate a lot and do some calculations there, and that Jacob gave you an instrument. Check if you still have it.
Completed: It looks like a logarithmic meter, but an upgraded one. You’re saying you used it to try and calculate the location of the City of Shadows, but it was constantly changing?