Tomas Slancik

The frame in timeshift is the frame at which you want to evaluate the input geometry

So if you want the frame 1 to start at 21 then you need to use $F-20

Since then when you are at frame 21 it will evaluate the frame 1 (21-20) of your input geo

You can also use Retime SOP to do some common time manipulation like in your case Shift Range

aeonzeon
I was under the impression that in VEX, variables are passed by reference.

they are passed by reference to functions when used as arguments

but assignment using = will pass evaluated value

jackdon4682
But I'm a little confused that I find nothing with 3@transform in official manual,

It's listed here, it can be 3x3 or 4x4 matrix
https://www.sidefx.com/docs/houdini/copy/instanceattrs#attributes [www.sidefx.com]