I wanted to write a script to check my RAM usage at regular intervals and then calculate its maximum.

To calculate the used Memory, I had two options, via neofetch or free -m

The output of $ free -m gives:

              total        used        free      shared  buff/cache   available

Mem:          15839        4169        7630         794        4039       10555

Swap:          2047           0        2047

So, I piped the output as $ free -m | grep Mem | awk '{print ($3/1024)}' which results in 4.07324 .

Now, if I do something similar to $neofetch output as, $ neofetch | grep -i Memory | awk '{print ($2/1024)}', I get the output as 4.84668

Thus, these 2 outputs do not match up, which one is to be considered for checking the actual RAM usage?
If it matters, I have a 4gb GTX1650 running Nvidia drivers, and consuming 53MB RAM when checked via $ nvidia-smi

One of the possible situations I can think of, is where $ neofetch gives me the Used memory and the shared memory, since the outputs of

$ free -m | grep Mem | awk '{print (($3+$5)/1024)}'

and

$ neofetch | grep -i Memory | awk '{print ($2/1024)}'

are very close to each other (4.85547 and 4.86035)

But my question remains, which memory values to trust?