Order of additive elements changes output

[default5tw6sffuxdm1]

I'm writing a small javascript to automate file setup, and part of it needs to copy one section of the file onto another area.  The second selection is dependent on the size of the file, so I did some simple addition to find the right location:

51.5-(startWidth+1.5), where startWidth is assigned from app.activeDocument.width

If startWidth is 18, it should add up to 32, but when passed into a prompt to check I noticed it was actually -32 inches.

And even more strange, if I change the order of operations to -(startWidth+1.5)+51, it calculates correctly to 32 inches

Does anyone know what could be causing this?

Using Photoshop 2023 on Mac OS Big Sur

Thanks!

[Stephen Marsh]

Have you explicitly set inches as the required ruler units?

[default5tw6sffuxdm1]

Yes, for both ruler and type.  

[r-bin]

Show the full code, including the one where you use "passed into a prompt".

[default5tw6sffuxdm1]

Here's the most relevant pieces, just tested it myself on a 20x20 blank new file

app.preferences.rulerUnits = Units.INCHES

app.preferences.TypeUnits = Units.INCHES

fileWidth = app.activeDocument.width

prompt(-(fileWidth)+51.5)

prompt(51.5-fileWidth)

The prompts give a positive number for one, and a negative for the other... but mathematically there should be no difference

[r-bin]

app.preferences.rulerUnits = Units.INCHES
app.preferences.TypeUnits = Units.INCHES

fileWidth = app.activeDocument.width.value

alert(fileWidth)

prompt("This is the title (hint). The result is below the line.", -(fileWidth)+51.5)
prompt("This is the title (hint). The result is below the line.", 51.5-fileWidth)

[default5tw6sffuxdm1]

Thanks!

Pulling the unitless value fixes the issue.

Still curious why the units would cause it in the first place...

[r-bin]

Most likely this is a bug. According to the documentation, this should not be the case.