Does Surface Flatness Matter for Gaming Mice? (Understanding how the gaming mouse's base, mousepad, sensor, and mouse skates interact)

October 10, 2022

Lately, there is more discussion about the flatness of the gaming mouse's base. Finalmouse specifically mentioned the base's flatness as a selling point of the Starlight-12 TenZ mouse. This article explores the importance of all this.

Why it matters

Flatness is all part of the design of a computer mouse. There are two main things that are influenced by surface flatness:

The glide of the mouse across a mousepad.
The sensor's tracking ability.

You might already be thinking it's time to check the flatness of your own mouse's base. But that's not the full story. There are other factors that play into this. What about the mouse skates? (We know this matters to our customers, so we measure the skates of a set to be within hundredths of a millimeter in height from each other.) Once again, there's more to the story.

Regarding the sensor's tracking ability, the good news is that it doesn't matter too much. A modern gaming mouse sensor is remarkably good at tracking. That's because it works by taking a series of images from the surface and then determining the input based off of the imaging.

You can see for yourself from Pixart's data. The soft pad, which you might expect to be a less flat surface, doesn't always result in less path error.

In fact, at the right Z-height, it will have less path error than a hard surface. The sensor takes into account these factors in its design (also the user should take into account the elastic deformations of the material which result in a lower Z-height to some degree.)

Factors that influence flatness and parallelism

Unless you are a flat-earther, you would know that the earth is definitely a "not flat" surface. The good news is that it doesn't matter for this discussion on surface flatness.

Factors that do matter:

The flatness of the table.
Flatness of the mousepad.
Flatness of the mouse base.
Evenness of the mouse skates.

When you have many variables interacting, it already complicates things. I once saw a disclaimer on Lethal Gaming Gear's glass skates about mouse base flatness, and it was good to see them shed light on this issue. The thing is, perfect flatness is impossible to attain. But even if you did, you have to factor in parallelism.

Parallelism: does it matter more than flatness?

If you have two perfectly flat planes, but one of them is off-axis, you have a problem. Your mouse would cut into the surface like a blade. Surface flatness is flat in respect to itself. Parallelism is flatness in respect to another surface. Parallelism is what ultimately matters.

At the end of the day, there are just 2 surfaces that come into contact when gliding your mouse: the mouse skates and the mouse pad. As mentioned before, small deviations will not result in a loss of sensor tracking accuracy.

Mouse Skates: the source of the problem or the solution?

Ask yourself why a mouse uses mouse skates to begin with. Why doesn't a mouse just have a flat and smooth base? I believe part of the answer (to be clear, there are several reasons) to this is because of surface flatness and parallelism. It's much harder to have the entire base be parallel to the surface (mousepad). It might be parallel in the X-axis, but not in the Y-axis.

PTFE is one band-aid solution to the issue. PTFE works as lubricated sliding as opposed to dry sliding. Essentially, PTFE is the solid form of an oil (if you are familiar with Krytox, it's liquid PTFE).

The design of Sapphireskates is such that the skates are going to evenly make contact, even without perfect surface flatness. That is simply due to the anatomy of its domed shape.

The tradeoff here is reduced support which can result in the incidence of "dig" if you tend to apply a lot of downward pressure on your mouse. However, mice are designed to slide horizontally, not vertically. And it can be mitigated with adding another set.

Selecting the right surface pairing is also important. Typically, you will match an elastic surface to a rigid one. For example, those who use a glass mousepad will want to pair it with something like PTFE. Whereas sapphire mouse skates should be paired with a cloth or plastic (which is still semi-elastic).

You might be wondering, are these still just band-aid solutions? Is the holy grail two perfectly flat and parallel surfaces? I would argue that it is not. The way that people use their gaming mice typically involves applying an uneven amount of pressure. You also must account for lift-off and landing. Perfectly flat and parallel becomes immediately problematic the moment you lift off your mouse. A dome, on the other hand, lets you do this freely - you can raise and pivot the mouse as you please.

This is not to say that flatness doesn't matter either. That's why we also have been developing flat-top shapes and are testing even more.

The mouse skates can be a source of optimization. Ken from our team does this to his own mice by stacking adhesives on certain pieces to balance out any unevenness of the mouse base.

Further Discussion: Surface Roughness

Another aspect to consider is surface roughness, which is different than flatness. It plays a major role in the low-friction performance when paired with a typical mouse surface. Some mouse skates reduce roughness via surface coatings. We achieve a smooth surface through rigorous polishing. But it's a topic large enough that it should be covered in a separate article.

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