To answer some private messages I have been getting,
going to Post it here so everyone can see and save me from having to send it over and over :)
The place mats I use are a firm rigidity plastic, 3D effect.
Sticker on the back says "Lenticular Placemat" 17"x11" 1/2 or 43x29cm
The blue sticks shown on the sides of the placemats, I buy at my local "Staples store" only place I can find them around here.
The pkg says "Slide grip report covers".
The first thing I do is trim these blue slide grips so they fit firmly under the inside lip of the fish tank.
Next I put the placemat up next to the tanks side and mark it for cutting, ( I bent the placemat a tad so you could see the mark)
Then I take it to my work table and trim it off along the line, then using the height of the sliders I trim of the top. So you end up with this.
Once you've done that I cut out the remaining section of the placemat to make another section.
this is what you should have now.
Next place the two cut out pieces of the placemat overtop of each other and slip on the sliders. So you have the same as the picture shows.
Next place it in the tank and see how it fits, This is the part where measuring doesn't always work out so well for me, So I trim of just a tad and keep trying until it fits snugly, and the blue sides snaps under the lip of the tank.
I have found that each tank can differ ever so slightly, So I do it this way for every tank I do.
I find it works better, tighter fit,...
I'm not very good at describing things, So I hope this helps somewhat..