OG is off even after pre Boil and Boil volume is spot on

[Big Al]

Ok so I had a preboil volume of 6.9 Gallons and gravity of 1.058. Took that with a sample and old fashioned Hydrometer. Into the fermenter at 6 gallons and my tilt says it’s 1.056 OG. I’m stumped and yes I calibrated in water before I dropped it in. Any thoughts on where my issue is other than I suck at reading an old Hydrometer?

 

[marc1]

Either you're off with your gravity measurements or you're off with your volume measurements. Or both.
Did you top up with water at all?

 

[Big Al]

I did not. I did take the draw from the pump in my grainfather which pulls from bottom and my guess is that the sugar content was higher there before I started the boil. Only plausible thing I can come up with at this point.

 

[dwhite60]

I did not. I did take the draw from the pump in my grainfather which pulls from bottom and my guess is that the sugar content was higher there before I started the boil. Only plausible thing I can come up with at this point.

This is probably it.

 

[codysorgenfrey]

I get wildly different readings if I take a sample from the bottom vs collecting all the runnings, stirring, then taking a sample. I bet that’s your issue.