This is a beautiful vintage stopwatch made by Excelsior Park.
Based on the images, here is a detailed breakdown of what I can tell you about it:
Maker: The dial clearly states "EXCELSIOR PARK" and "SWISS MADE." Excelsior Park was a renowned Swiss watch and movement manufacturer, famous for producing high-quality chronographs and stopwatches. They were especially well-regarded for their precise mechanical movements.
Type: It is a mechanical stopwatch (also known as a chronograph or timer).
Case: The case is chrome-plated or stainless steel and has a highly polished finish (with visible surface scratches consistent with use and age, as seen on the back). It features a large, fluted winding/start/stop crown at the top with a bow for attaching a lanyard or chain.
This is the most valuable and technically complex possibility.
Function: A split-seconds or rattrapante (French for "catch up") stopwatch is designed to time two separate events that start simultaneously.
The main crown starts both the main black second hand and a hidden second split-second hand (often red or white).
The side button stops one of the hands (the 'split' hand) to record an intermediate or 'lap' time, while the other hand continues to run.
Pressing the side button again causes the stopped hand to instantly "catch up" (rattraper) to the running hand.
Identification: If your stopwatch had this function, you would see two central seconds hands (one on top of the other, often black and green/red, or black and white) when you start it.
The dial is designed for precision timing and is known as a 1/5th second timer, as each second is divided into five increments.
Main Scale (Seconds): The large black hand tracks the seconds around the main, outer scale.
The outer track has indices for every 1/5th of a second.
The main numbers are in black (0, 2, 4, 6... 28, 30), marking every two seconds.
There is a secondary, inner set of numbers in red (32, 34, 36... 58, 60/0), which are likely intended for timing a full 60-second cycle or for tachymetric calculations, though it seems to simply continue the second count.
Register (Minutes): There is a small sub-dial at the 12 o'clock position (or center-top) that tracks the elapsed minutes.
It has numbers from 3, 6, 9, to 12 or 15. The presence of a small green hand suggests it's a 30-minute register, making the full timing capacity of the stopwatch 30 minutes.
Foundation: Excelsior Park was established in 1866 in Saint-Imier, Switzerland, originally as Jeanneret-Brehm & Cie.
Specialization: They gained a reputation for manufacturing high-quality, in-house mechanical movements, particularly for chronographs (stopwatches and chronograph wristwatches).
Notable Use: Excelsior Park movements were highly regarded and used by other famous brands, including Gallet and Zenith. They made military-issued pieces and stopwatches for various industries and sports.
Dating: Without seeing the movement or a specific model number, it is difficult to date precisely, but stopwatches of this style and with the Excelsior Park branding are typically from the mid-20th century (e.g., the 1940s to 1970s). The design is classic for that era.