"Retro Repair" key electronics skills?

[Jon Elson]

On 05/10/2016 02:33 PM, Bill Sudbrink wrote:
>> The other is that, as I said before, any ground
>> connection has impedance (it's the inductance that
>> is troublesome normally) so that points (say IC pins)
>> that are shown as grounded may actually have a
>> voltage difference between them.
> If I think about it too much, this gives me the
> willies, the same way.
>
>
I have a 3500 Lb Sheldon lathe.  During rebuilding of it, I 
got a very sensitive electronic level, to aid in making sure 
the bed was reground straight.  I found that when I walked 
from one end of the lathe to the other, it tilted about one 
arc second.  That was my weight deflecting the concrete 
floor of my basement, causing the lathe to tilt slightly.

All structures, including the earth, deflect under load.

Jon