See how mechanical-watch rate stability can change as the mainspring runs down across common 40–70 hour reserve ranges.
A fully wound mainspring delivers higher torque. As reserve falls, torque drops and some watches show more rate drift near the end of their power curve. Healthy design aims to keep usable stability across most of the reserve, but low-reserve variation is still common.
• Judge timing after normal wear, not only at the extreme end of reserve
• Long-reserve watches can still drift when nearly empty
• Big timing changes at all wind levels can indicate service needs
Why does my watch change accuracy as it winds down? Mainspring torque falls over the reserve, which can affect rate stability on many mechanical watches.
Is low-reserve drift normal? Some variation near empty can be normal. Persistent poor timing when fully wound is a bigger service concern.
Do 70-hour watches avoid this completely? No. Longer reserve helps usage patterns, but the end of the curve can still be less stable.
How should I test my watch? Wear or wind it normally for a few days and compare average rate, rather than judging only one low-reserve night.