: What causes Illustrator to lose Exactitude? See below image, then read on... Previously this circle was 76 pixels diameter. I changed it to 64 by manually entering it into the W: container,

@Sherry646

"Use Preview Bounds" is probably enabled.

I can recreate what's happened to you consistently by having this setting on.

If I turn "Use Preview Bounds" OFF ( ⌘K or ⌃K and UNCHECK "Use Preview Bounds"), then miscalculations such as this don't occur.

Also in my testing:


It doesn't matter if "Align New Objects to Pixel Grid" is turned ON
at document creation or I enable it per object in the Transform
palette (⇧F8), or I ignore it entirely
It doesn't matter if "Snap to Grid" is ON or OFF
It doesn't matter if Scale Strokes & Effects is ON or OFF
I can correct an object with this problem only by disabling "Use
Preview Bounds", then selecting the object, and then disabling
"Constrain Width and Height Proportions" and typing new values into
the Transform palette.
It happens to any path (simple, compound, or Pathfinder-created
compound)


My test went like this:
(Using Macintosh Illustrator CC 17.1.0):


No documents open, Illustrator > Preferences (⌘-K) > Use Preview
Bounds: OFF
Create a new document 100px × 100px, Units: Pixels, Color Mode: RGB,Raster Effects: 72ppi, Preview Mode: Default, Align New Objects to Pixel Grid: OFF
Draw a circle an arbitrary size (hit L and then Shift-Click-Drag).
Mine came out at 59.425 px
With "Constrain Width and Height Proportions" ON, adjust size of
circle using transform palette, so it's a true pixel dimension (I
chose 50px)
Hit ⌘-K (Illustrator > Preferences) and toggle the Use Preview
Bounds: ON. This resized my circle to be 51 px × 51 px.
Type a new Width in the Transform palette (Constrain Proportions
still on, I chose 30) and Tab to the next field, - in my case H was
set to 29.986px


And then I tried variants of of align to pixels etc…

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