In the properties window, UDim values will round to the nearest thousandth when the actual value is different. This makes working with UI more difficult and there will end up being rounding issues on bigger displays, making frames be off by a few pixels which can ruin the look of the UI
The properties window should show the full UDim value
Look at AbsoluteCellSize changing when a more accurate UDim value is entered, showing that its only being rounded in the properties window while the actual value is being used internally