A. Lange & Söhne

1815 Rattrapante Perpetual Calendar Watch

A complication that automatically knows and adjusts for the correct amount of days for every month the year, with the exception of February; the calendar function only needs to be adjusted once every year.

A small opening on a watch's dial that reveals a complication; this is typically the date, day, or month.

A self-winding movement that harnesses energy from both winding the watch and from the wearer's motion. To operate continuously, automatic watches require daily wear or a watch winder. If the watch stops, simply wind the crown clockwise 20 - 30 times, set the watch and resume wear.

The top part of the case that holds the crystal in place; bezels can be fixed in place or rotate and are typically of the same shape as the case.

A watch that displays time and provides stopwatch function.

Additional features on a watch other than basic timekeeping. Common examples are day, date, chronograph and moon phase.

Grade 0 watches are new or unworn, with no signs of wear or damage.

Grade 1 watches may possess any of the following aspects: • Imperfections that are superficial and consistent with handling • A single point of light marking • A bracelet that has been sized • A case that has been engraved.

Grade 2 watches may possess any of the following aspects: • Imperfections that are superficial and consistent with light use • Multiple points of light markings • A Single point of moderate marking • A bracelet with light stretching • Minor cosmetic alterations to external components.

Grade 3 watches may possess any of the following aspects: • Markings and wear that are consistent with moderate use • Multiple points of moderate markings • Light discoloration to metal, dial or hands • A bracelet with moderate stretching • Blemishes at crystal or embellishments • Cosmetic alterations to external components.

Grade 4 watches may possess any of the following aspects: • Markings and wear that are consistent with heavy use • Moderate wear at case and attachment • One or more points of heavy markings • Moderate discoloration to metal, dial or hands • A bracelet with heavy stretching • Moderate wear at crystal • Significant cosmetic alterations to external components.

Hour displayed through an aperture in the dial instead of a hand.

All watches require a full service every 4-6 years.

A watch movement that uses a mainspring to store energy rather than a battery and must be wound by hand and/or by physical motion.

A watch feature that tracks and displays the lunar phases throughout the month. The moonphase dial is typically displayed by an occluded aperture.

A complication that takes leap year into account and automatically adjusts the date for the every month throughout the year.

The amount of energy stored in a watch before it stops running. Some watches feature a power reserve indicator on the dial. Common mechanical movements typically have a power reserve of 36-48 hours, however in some more complicated watches the power reserve can range up to several days.

A watch feature allowing the wearer to change the date on the watch without moving the hands.

The pendulum inside an automatic mechanical watch that winds the mainspring. The rotor moves on a pivot with motion from the wearer’s wrist.

A watch dial design that exposes the internal movement. A skeletonized dial allows the wearer to observe some or all of the working parts inside of the watch. It may also be referred to as an “openwork” design.

A watch case shape featuring convex sides.

Water resistance determines how much pressure a watch can withstand; water resistance is a measure of pressure, not depth

Refers to warranty papers provided at the time of original purchase. Warranty may or may not still be active. Depending on the designer and year, this may be paperwork, a booklet, or a plastic card.

Additional items that accompany this watch. Collateral may included boxes, official sales warranty(commonly known as "papers"), reference materials, or additional components such as straps and links. Collateral can add value, but all watches undergo a full authentication process regardless of what is included.