Level as straight edge

[messmaker]

I was watching "Monk" and I remember this topic came up. He always checked for level but first he would check his level with his level checking level. He was questioned on how he knew that his level checking level was actually level. He replied that he took to the hardware store twice per year to have it calibrated.

[cgallery]

I used someone's suggestion and held a 100W trouble light behind them and wow I could see a gap here and there! But I tried to "poor man's feeler gauge" it with a sheet of paper (.0035" -that's 3.5 mils) and I could not even start to slide it through the gap where I saw the light.

I had two Starrett 12" combination blades that were brand new and were supposed to be straight to some incredibly high standard.

So I held them next to each other (on a piece of glass) and held that up to the sunlight and could see light passing gaps. "Oh no!" I remember thinking, "these aren't straight."

But after studying the problem a little I discovered I could not fit even my finest feeler gauges between them.

I don't know what else to conclude other than light is nature's finest feeler gauge.

[LCHIEN]

I had two Starrett 12" combination blades that were brand new and were supposed to be straight to some incredibly high standard.

So I held them next to each other (on a piece of glass) and held that up to the sunlight and could see light passing gaps. "Oh no!" I remember thinking, "these aren't straight."

But after studying the problem a little I discovered I could not fit even my finest feeler gauges between them.

I don't know what else to conclude other than light is nature's finest feeler gauge.

Wavelengths of visible light are about 600 microns (red end of spectrum) which is very tiny, so yes it can go thru very small cracks.

[Kerf]

Wavelengths of visible light are about 600 microns (red end of spectrum) which is very tiny, so yes it can go thru very small cracks.

Very interesting....

[LCHIEN]

I was watching "Monk" and I remember this topic came up. He always checked for level but first he would check his level with his level checking level. He was questioned on how he knew that his level checking level was actually level. He replied that he took to the hardware store twice per year to have it calibrated.

I'll bet in real life they would take his money and level, do nothing, call him back a week later and say its in spec, you can come and pick it up!