You could buy a laser for tiling which has a horizontal laser on the bottom. Huepar has one on Amazon: Huepar Laser Level Self-leveling 4x360 with Remote Control 16 Lines Green Beam up to100Ft, 4D Cross Line Tiling Floor Laser Tool, Magnetic Bracket, 5200mAh Li-ion battery 6-12 Hours Working Time-904DG https://www.amazon.com/dp/B098QPM5Z3/ref=cm_sw_r_cp_api_i_ZNQTV4Z9EYPP2RGB9R6P