The 9-Section Acrylic Production Slate with Color Clapper Sticks from Elvid is a production slate made of white acrylic designed to be used with dry erase markers. It uses standard-size color clapper sticks to provide visual and audio sync points when using a separate device to record audio (dual-system sound). The full slate measures 9.25 x 11" and features engraved text and lines.
 
https://www.bhphotovideo.com/c/product/1030772-REG/elvid_ps_911_c_9x11_acrylic_dry_erase.html