The Topo mat "calculated terrain" feature provides its own hills & slopes for a varied, ergonomic, and comfortable standing surface.
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Topo by Ergodriven The Not-Flat Standing Desk Anti-Fatigue Mat
Topo Comfort Mat by Ergodriven, The Original Not-Flat Anti-Fatigue Standing Desk Mat with Calculated Terrain, Accessories
Standing desk users NEED this!