A TRAVEL DOWN MEMORY LANE.....
1948 : 3-6-1, "ball must be put in play 25 seconds after it is ready"
Field judge (now line judge) kept game clock , few scoreboards in town. 4 minute warning before end of each half. Ref kept play clock, some by their watch, some by counting, some by guessing.
Bake sales began to produce scoreboards, field judge was happy

, ref could now take play clock from scoreboard IF he was facing and good at math.
ReadyRef was invented.
Back Judge was born, refs often presented BJ s their ReadyRef in an off-field ceremony.
2019 : 3-6-1, added the 40 second play clock.
10/24/1945 : Both the United Nations and myself were born (unsure which will last the longest). During that timeframe, I've never had a coach,fan,scribe, player, parent, official or talking dog ask : "GEE, I WISH WE HAD A VISABLE PLAY CLOCK

'