I do something simular..I insert or draw and item and the use the
scale command, selecting what I want scaled and use "(/ 1 25.4)" for
the amount to scale:
Select objects: c
Specify first corner: Specify opposite corner: 4 found
Specify base point:
Specify scale factor or [Reference]: (/ 1 25.4)
You can, but AutoCAD only understands drawing units.
If you start drawing with inches as the drawing unit and then want to
switch to millimetres as the drawing unit, you will have to scale
everything up by 25.4 so that an object that was 1 unit (inch) now is
25.4 units (millimetres).
You need to be aware that each time you scale up and back, you run the
risk of introducing small errors. The more you do this, the worse it
will get because there will be rounding and it all adds up.
If you use "25.4" or it's inverse "10/254" there will be no measurable
error, even after thousands of rescalings. They are exact.
Errors will happen if you try to use ".03937" or any similar decimal
as the inverse because they are not exact.
Well, I have had survey information get screwed up and that was only
scaling up and back by 1000 to go from metres to millimetres and back.
The particular boundary ended up being scaled a few times and before
long errors started creeping in. After that it became standard practice
to do the boundary in metres, then copy it and scale the copy up. If it
needed to be altered because of new survey data, the original boundary
was modified, then copied and the copy scaled with the previous boundary
You're either A) Running an add-on that intercepts the scale call,
B)Running a boundary about 30 times the size of the solar system, or
somebody's finger slipped on the keyboard. <G>
Autocad uses signed double precision floating numbers (AKA (64bit IEEE
reals), where one bit is the (+/-) sign, 52 bits are the mantissa (0
thru 4,503,599,627,370,496) and 11 bits are the exponent -1023 to
+1023. On a 4 km boundary the accuracy is 0.000000001mm.
Autocad has many faults; but math precision is not one.
A very old (1983?) drawing of the solar system demonstrating the huge
dynamic range inherent in the 64-bit math.
http://www.intelcad.com/pages/autocad/solar.dwg (10,292 bytes)
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