In a small exercise book, the 77-year-old electrician writes out by hand a line-by-line record of shelling attacks and casualties - which buildings were hit, who was killed, who was wounded.
"Sooner or later, you may need proof: this is what happened, or didn't happen, during the war. This is why I write it down: it's history. And history is fair and trustworthy," he said, running a finger across a page of entries.
Like many people caught up in the conflict between Ukrainian government forces and Russian-backed separatists, Cherkas has ties to both nations - his mother was Russian and his father Ukrainian. "My soul is both, Ukrainian and Russian," he said.
He has a Ukrainian passport, but his first language is Russian.
But living on the edge of Donetsk, one of the two main strongholds of the separatist side, he says his allegiance is firmly with Russia. He gets his news from Russian state TV on a set in the corner of the room with a miniature triptych of icons perched on top.
No surprise, then, that he disbelieves the Ukrainian government's warning that Russia has more than 90,000 troops near the Ukrainian border and may be poised for a full-scale invasion - something the Kremlin denies.