Gravity reading issues help

[ChuckCollins]

I crush my own grains and am very pleased with where I have it, and I use
brew smith as a guide and my Est Mash Efficiency is always from lower 70 to low 90's and I am usually hitting my numbers on pre boil gravity and OG but when I do my hydrometer reading I am not always hitting my final numbers but close,my hydrometer is a basic one and it is a little off I know, but kind of puzzled on it, but there is times when I am dead on… it is a roller coaster of gravity reading…

 

[Ondori]

What temp is the sample that you are testing? 68 degrees is the suggested on mine. Over or under that and you have to subtract or add points.

 

[ChuckCollins]

I will start taking the temps at the final I do it with the pre boil and before I pitch my yeast.. thanks