sketch. Different spacing between columns?

Question

Sketch

Help me understand the Sketch grid settings.
For any given parameters, the grid is drawn crookedly - indents between columns of different widths. Marked in red in the photo below. If you use a grid in the layout, then the width of the columns and elements are not the same. I can't work properly. You have to check everything on a calculator and work without a grid at all.
An example is you numbers. The column width is 102, between the columns 4. If you display the block in three columns on the grid that Sketch creates, then the block width will be 313. And according to the calculator, it should be 314 (102+4+102+4+102)!

Answer 1

If I'm not mistaken, you have given the wrong number - you can't divide 1900 into 18 columns with a gap of 4px, here's the sketch and adjusts with rounding. Try to take a width of 1904 (18*102+4*17)
ps and to be precise, this is not a grid))