The transformers change either primary or secondary voltage level at times (1,2,3).
trafo1 primary voltage levels (1, 0.9, 1, 1.1)*V_nom_prim trafo2 secondary voltage levels (1, 0.9, 1, 1.1)*V_nom_primNote that the primary voltage source is fixed.
See for example:
meter 12.v voltage secondary, if primary is changed at fixed source. meter 22.v voltage secondary, if secondary is changed at fixed source.