Sypon refractometer

[Blue Ring Octopus]

So I just bought this refractor and I treat it really good, when I am done with it I clean it and put it back in the case, and then I put it back in the box, so today I am using it and it seems that I am seeing through a donut hole and through that the scale, so has this happened to anyone else?

 

[vetteguy53081]

How are you cleaning it and using what to clean it ?
Calibrate it occasionally also

 

[Blue Ring Octopus]

I use the cloth that comes with the unit, it comes pre-calibrated and I have used it a couple of times. It is weird to see the little ring within the viewer, makes it hard to see anything. Think of a target, with the rings going to the center that is what it is like.