Check your dipstick

[fruitcakesa]

I checked the oil in the 81 today and found it was a quart down so I added that much and then headed down the road to my daughters soccer scrimmage about 25 miles away.
About 5 miles out I noticed the oil pressure guage was behaving very erratically; dropping to 1 then slowly climbing back to 3 , repeatedly.
I got a bit concerned and stopped in the next town and opened the hood to find the dipstick was not fully seated in the dip tube by about 1/2" or so.
I pushed it completely in and restarted the motor and thankfully that put an end to the flucuating guage.
Anybody have an explanation for this?