GROMA (greek., latin groma) is a measuring instrument for fixation of the North-South line by the solstice in the given point, construction of the West-East line and weighting parallels to both lines, which was necessary for marking-out the field camps.

1 — portable instrument with the rotary slat-nozzle (2); 3 — angle cross with the sight thread A-B and C-D rotating around the plumb axis (4); 5 — foundation with the cross drawn on the stone: a-b — longitudinal axis, c-d — diametrical axis of the field camp.