A Person Loopback Test is an observation about yourself that tells you things you wouldn't otherwise notice.

Two examples of tests that I do come to mind:

	* I know some music so well that I have an exact copy in my head. When I'm listening to that music, it sometimes sounds faster or slower. When it sounds faster, I should sleep, when it sounds slower, I should code or do some other mentally demanding task.

	 :	''When I wake up in the morning, music always sounds really fast to me... should I go to sleep then? ;-)''

	* When I start to feel particularly happy, or particularly sad, I think back over the last few minutes and hours to see if my emotions have been switching without external input. If I'm on a five minute rollercoaster, it generally means I've been eating food I'm allergic to, or that I should eat some food. If I'm just irritable for no reason, it generally means I have a cold.

While discussing this with a few people on IRC, I found out that they don't do these loopback tests. One of these people did mention that RichardFeynman tested his own counting speed at different times though.

Do you do any PersonalLoopbackTests? If so, what are they?
-- ShaeErisson

Should I have named this page PersonalUnitTests? :) -- shae

------

I have a loopback test for too-tired-to-drive. I don't use cruise control on long drives, and I drive a manual, which makes it extremely easy to maintain exactly the speed I want. I make it a habit to stay within one mph of my desired speed - this is how the anal retentive have fun on the road.

	* I find that when I'm too tired, I lose the ability to stay close to the desired speed. I suddenly notice that I'm going 5mph slower or faster than I want. Both times in my life when I nodded off at the wheel, I stopped being able to hold a constant speed perhaps 15 or 30 minutes before that.

So now, when I find myself unable to hold a constant speed, I pull over and rest.

My theory is that when I'm tired I lose the ability to rapidly scan the road, instruments, and mirrors, and start fixating on one thing. Hence the speedometer goes unobserved for too long and my speed drifts. Unconsciousness is not far behind once that happens.

This technique may not apply as well to cars with automatic transmissions. I find it much harder to maintain a constant speed in them. They do work differently, but it could also be that I'm just not used to them. -- WayneConrad

My mother was once pulled over late at night by the Florida state police. Her offense: she was slow to dim her headlights. The officer explained that that was a sign of fatigue and that she should consider stopping for the night. -- WardCunningham

I was driving home from my printing job on second shift one night when I noticed a trooper behind me. Concerned that I might exceed the speed limit, I kept checking the gauge frequently. Approaching my home, he pulled me over. My attention to the gauge led to an unnoticed inattention to the solid line down the middle of the road. He thought I might be intoxicated. I guess I was just tired. In any event, I was looping back too much. -- WaldenMathews

This is a very important thing to have a loopback test for... I have one: I play a 9x9 game of Go against the computer and look at the final score. Takes perhaps ten minutes, but quite accurate. Still need a good way to measure reflexes though - perhaps PacMan?
----

	* When I don't enjoying reading or talking about the industry, I find it is because I am working to much (FortyHourWeek). -- ErikMeade

When I start thinking about changing fields, I know it is time to get a new job.

Also

When I am drinking and the tip of my nose gets numb, I stop drinking and do not drive until I can feel all of my nose again. If my teeth go numb, I don't drive until the next day. -- KenMegill

----
I fire up Windows Minesweeper on "Expert", and see how far I get without pausing to think "too much". A couple of rounds is usually enough to confirm whether mental fatigue or short attention span has set in.

'''What's the difference between fatigue and a temporary short attention span in that case?'''
----
Sometimes when I can't quite make a decision between two things, I'll pull out a coin to flip, and assign a choice to each side. I'll give it a big flip, call it in the air, and ''ignore the result'': I'll usually have a quick flash of hope that it comes up a certain way, and I go with ''that''. -- SckotVokes