Fluid level marker / Tool for those with asthenopia

By the use of the product you can prevent the overflow of the fluid filled into the glass.When using we place the product onto the glass/pot with the hook.We catch it on the correct place and at the same time we begin to fill in the fluid with our other hand. In the course of the rise of the fluid the thin walled hollow plastic ball put into the fluid is raising together with the fluid,as a consequence of which the small ball on the opposite side comes lower and touches our thumb holding the level marker, which shows us that the glass/pot is full.Size of the device:50x60x20mm.Material of the balls: ABS
Material of the holder:Stainless steel.