Which is Accurate?

Ubuntu Mate 16.04 is high on memory usage.

I use the Mate System Monitor and Htop to track my resource usage.

I notice that Mate System Monitor displays a higher amount of memory being used than the amount of memory that Htop displays being used.

The difference between the two monitors can be 150MB to 250MB.

My question is which monitor is displaying the true memory usage.

Thanks