How to use $myInvocation to do simple command profiling in PowerShell

One of the things I’ve noticed on our internal PowerShell DL is that some of the Redmond cognoscenti like to have the history ID in their PowerShell prompt and I was never sure how they did it. 
Then the other day I noticed it was part of the $MyInvocation automatic variable, so it is easy enough to add that to the prompt function - in case you didn't know PowerShell calculates the prompt with a function, so all kinds of creativity can be deployed there.

Over the last day or so I have been playing with some stuff in PowerShell which takes a long time to run. My old university tutor would be glad that I worked out the algorithm I’m using will take Order n-cubed time to run. I can’t see an improvement to the overall way of solving the problem, but I can put some short cuts in. What I wanted to know was whether it would run any quicker. One neglected part of the History in PowerShell is that that gives you start and end execution time, so I ended up doing this

h    #Alias for get-History

note the last number for example 123,

$hh=h 123 $hh.EndExecutionTime.Subtract($hh.StartExecutionTime)

Putting the history item in a variable lets me use [tab[ to expand the EndExecutionTime , Subtract and StartExecutionTime so it actually saves typing

Thinking about $MyInvocation.History, I realized I could automate this, and just added the following to my profile

function howLongWasthat {
  (get-history ($MyInvocation.HistoryId -1)).endexecutiontime.subtract((get-history ($MyInvocation.HistoryId -1)).startexecutiontime).totalseconds
}

So now after running a command I type how [tab] [enter] and hey presto it gives me the run time. 

Following on from my previous post , do you have any magic profile entries to share ?