# mesh / region creation in unit meters or mm:

How can we know the unit of mesh or create a mesh in specified length units:

such as, for example I have:

    bmesh = ToBoundaryMesh[
"Coordinates" -> {{0, 0}, {1, 0}, {1, 1}, {0, 1}, {1/6, 1/6}, {5/6,
1/6}, {5/6, 5/6}},
"BoundaryElements" -> {LineElement[{{1, 2}, {2, 3}, {3, 4}, {4,
1}}], LineElement[{{5, 6}, {6, 7}}]}];
bmesh["Wireframe"]


How can I specify the length of the mesh and/or boundaries in meter or mm or cm units:

 mesh = ToElementMesh[bmesh, MaxCellMeasure -> Infinity];
mesh["Wireframe"]


is there a way or am I missing some basics?

The numbers "Coordinates", without any unit, define your mesh.

One way to get a mm-mesh : Introduce pseudo units meter,mm

Needs["NDSolveFEM"]
meter=1;
mm=meter/1000;

bmesh = ToBoundaryMesh[
"Coordinates" -> mm {{0, 0}, {1, 0}, {1, 1}, {0, 1}, {1/6, 1/6}, {5/6, 1/6}, {5/6,5/6}}, "BoundaryElements" -> {LineElement[{{1, 2}, {2, 3}, {3,4}, {4, 1}}], LineElement[{{5, 6}, {6, 7}}]}];
Show[bmesh["Wireframe"], Axes -> True]


mesh = ToElementMesh[bmesh, MaxCellMeasure -> mm^2/100];
mesh["Wireframe"]


Hope it helps!