What Does the Negative Sign Indicate in the Mo Formula on HyperPhysics?

[Audaciity]

Homework Statement

At this site http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/micros.html , what does the negative sign indicate in the Mo formula?

Homework Equations

On website

The Attempt at a Solution

My guess is that either L or Fo are negative, but a negative magnification makes no sense, so basically it is a substitute for a modulus. Note: negative magnification could not possibly mean the image is diminished, because a diminished image simply has a magnification of less than 1 but greater than 0.

 

[rl.bhat]

It may be because of the sign convention. Here the object and image are in the opposite direction of the axis.

 

[Audaciity]

I don't believe either measurement qualifies as virtual