Question: I have a script where I keep time of when I start and finish. This code works on Linux, but not on my MacOS Sierra v 10.12.6

```
start=`date +"%a %b %d %Y %r"`
end=`date +"%a %b %d %Y %r"`
elapsed_time=`date -d @$(( $(date -d "$end" +%s) - $(date -d "$start" +%s) )) -u +'%H:%M:%S'`

```

The error I get is: 

```
usage: date [-jnRu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ... 
        [-f fmt date | [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]
usage: date [-jnRu] [-d dst] [-r seconds] [-t west] [-v[+|-]val[ymwdHMS]] ... 
        [-f fmt date | [[[mm]dd]HH]MM[[cc]yy][.ss]] [+format]
-bash: - : syntax error: operand expected (error token is " ")

```

Is there a way to change this so that it works on my Mac?

Answer: 
**Yes**, you definitely **can track moving surfaces and moving objects** in `ARCore`. 

If you track static surface using `ARCore` – the resulted features are mainly suitable for so-called `Camera Tracking`. If you track moving object/surface – the resulted features are mostly suitable for `Object Tracking`. 

You also can mask moving/not-moving parts of the image and, of course, inverse Six-Degrees-Of-Freedom (translate `xyz` and rotate `xyz`) camera transform.

> 
> Watch [this video](https://www.reddit.com/r/oculus/comments/70tz8p/instead_of_tracking_the_static_environment_in/) to find out how they succeeded.
> 
> 
> 

[![enter image description here](https://i.stack.imgur.com/agUy4.jpg)](https://i.stack.imgur.com/agUy4.jpg)
I guess it should be possible theoretically. 

However, Ive tested it with some stuff in my HOUSE (running S8 and an app with unity and arcore) 
and the problem is more or less that it refuses to even start tracking movable things like books and plates etc:

due to the feature points of the surrounding floor etc it always picks up on those first.

Edit: did some more testing and i Managed to get it to track a bed sheet, it does However not adjust to any movement. Meaning as of now the plane stays fixed allthough i saw some wobbling but i guess that Was because it tried to adjust the Positioning of the plane once it's original Feature points where moved.