Instruction: Answer the given question using the supporting document.

Input:
Question: What is the mug's diameter at its base?
Document: The fairly soft plastic of the lid is dinged up a little, but no breakage or leaking, and since the plastic is so soft, these dings smooth out over time and use.- The cup has a wide base (about 3 3/16"). It doesn't fit in many cupholders; even if the cupholder is wide enough to accommodate the base, the handle might get in the way.
The trail of tea was coming from tab in the center of the lid. I'm not sure how that happened but suffice it to say this is not recommended as a travel mug. I definitely would not toss it into a backpack.The base is also just ever so slightly too big for the cup holder in my center console. I can force it in just far enough so it will wedge itself in but, not an ideal situation. It obviously can (and did) pop out.
I have been looking for some time for a small stainless vacuum mug for my Keurig Mini brewer (Model B30), and this is (almost) perfect! The vacuum insulation keeps my coffee hot for a lot longer than it takes me to drink it and everything  is very high quality.Unlike my beloved 20 oz. Thermos mug (that is way too big to fit in the Keurig) there are no hidden seals in the base assembly  to get yucky. All plastic parts and seals are in the removable top.
the handle is on the top part, not easy to use, it leaks and you can't use if ur a lefty..
You can't put this inside your backpack when it has liquid inside - but see next item.- Open-handled mug. I specifically looked for this design because I can slip the handle into a D-ring of a backpack or briefcase, very convenient when I have my hands otherwise full, e.g. with an umbrella and said briefcase. No problems leaking or sliding out of the D-ring even with a full mug.- Not too big. I am not a heavy coffee drinker.
Within the Contigo brand this is definitely my favorite model.For Aeropress users on the go, look no further. Buy 2 of these so you'll always have a clean one.
While this product is well made is doesn't come close to living up to it's promises. The product description claims that this cup will keep beverages hot for four hours. This might be true if it's sitting in the equatorial sun at noon. However, even with preheating the cup with hot water first, it doesn't even keep coffee hot for one hour. After 30 minutes coffee is only luke warm. Pretty disappointing if you like hot coffee.
Tonight I stepped out of my vehicle and when I returned the mug had taken my place in the driver's seat. Upside down of course. It was night and I have tan seats so when I grabbed the mug I didn't notice a wet spot, but when I sat down I knew there was one. At least on the seat of my pants at this point. I had assumed the button had been momentarily depressed (as was I) when the lid/handle made impact with the seat.
This mug was a disappointment. The lid has a very unusual design intended to prevent accidents. Yet one time, there was coffee leaking through the handle into my lap. Also, when you take a drink, the flow of coffee through the spout is slower that my old mug (which also had a spout to avoid accidents). Lastly, the design of the lever that you need to use each time you take a drink is a bit inconvenient.
This mug really surpassed my expectations. It keeps my coffee hot for hours from its thermal properties and the lid being completely sealed really keeps the heat in. The first few times I press the button to take a sip there is even a pressure relief pop. I might grab a second one of these just in case the mechanism ever wears out.
Answer: I make it as 84mm +/- 1mm