A good alternative to the Heuer Dash clocks. The 8 Day clock is standard in most General Aviation Aircrafts, even today. Some also have a radial pointer that can be set as a reminder over the minute hand to allow simple elapsed timing.

Clocks incorporating the stopwatch function (Chronographs) were required equipment in Transport Category Aircrafts. They were used for various timing events during starting engines, checking groundspeed, holding patterns and most of all, timing approaches from the final approach fix to the runway or missed approach point.
In more modern, late model Aircrafts, these clocks have been replaced with Quartz-Digital Display clocks.

As some of these older aircraft are being phased out or upgraded, these clocks become surplus items. There are a number of companies that sell these clocks in the aviation market.
So, anyone interested in these very accurate and well calibrated clocks can find them in aviation surplus stores.