Preheat your kitchen to a cozy warmth. Line a 9×13 inch baking dish with parchment paper, ensuring the paper hangs over the edges for easy removal later. Spray the parchment thoroughly with non-stick cooking spray.

Melt 3 tablespoons of butter over low heat in a large saucepan. Once melted, add a 10 oz bag of mini marshmallows. Stir constantly until the marshmallows are fully melted and smooth, about 5 minutes.

Pour in 6 cups of Rice Krispies cereal into the melted marshmallow mixture. Gently fold the cereal until well-coated. This should take about 2-3 minutes.

Divide the mixture into three equal portions. Leave one plain, add red gel food coloring to the second, and yellow coloring to the last. Stir until each color is vibrant.

Press the red mixture into the bottom third of the prepared baking dish. Sprinkle the yellow mixture into the center third, and top with the uncolored mixture. Allow to cool completely for about 30 minutes.

Once firm, slice into long rectangle bars resembling rulers, about 1 inch wide for uniformity.

Melt ½ cup of white candy melts and ½ cup of chocolate chips in separate microwave-safe bowls, stirring every 30 seconds until smooth.

Using a piping bag or spoon, add ruler markings with melted chocolate onto one side of each treat. Drizzle melted white candy melts along the other side to create a 'metal edge.'

Add numbers and small lines on your Ruler Rice Krispies with black decorating gel or a black edible marker.

Allow the decorated Ruler Rice Krispies to set fully before serving or wrapping. This ensures the coatings have hardened and are easy to handle.