b'\n_START_ARTICLE_\nJam besar berdiri\n_START_PARAGRAPH_\nSebuah jam besar berdiri, juga "jam peti panjang" atau "jam datuk", ialah sebuah jam batu ladung berdiri sendiri yang digerakkan oleh pemberat, dengan batu ladung digantung di dalam menara, atau pinggang peti jam. Peti jenis ini umumnya sekitar 1.8-2.4m (6-8 kaki) tinggi. Peti ini sering dihias secara terperinci dengan ukiran pada hud, atau bonet, yang mengelilingi dan membingkai dail, atau muka jam. Pembuat jam Inggeris William Clement dikreditkan sebagai pengembang bentuk ini pada 1670. Kebanyakan jam besar berdiri merupakan jam berbunyi, yang bermakna mereka membunyikan waktu pada setiap jam atau pecahan satu jam._NEWLINE_Istilah "jam datuk", "jam nenek", dan "jam cucu perempuan" telah digunakan untuk merujuk kepada jam besar berdiri. Walaupun tiada perbezaan khusus di kalangan istilah-istilah ini, pandangan umum menyatakan bahawa sebuah jam yang lebih kecil daripada 1.5 m (5 kaki) ialah jam cucu perempuan; 1.5m (5 kaki) ke atas ialah jam nenek; dan 1.8m (6 kaki) ke atas ialah jam datuk.\n_START_SECTION_\nPenerangan\n_START_PARAGRAPH_\nTraditionally, longcase clocks were made with two types of movement: eight-day and one-day (30-hour) movements. A clock with an eight-day movement required winding only once a week, while generally less expensive 30-hour clocks had to be wound every day. Eight-day clocks are often driven by two weights - one driving the pendulum and the other the striking mechanism, which usually consisted of a bell or chimes. Such movements usually have two keyholes on either side of the dial to wind each one (as can be seen in the Thomas Ross clock above). By contrast, 30-hour clocks often had a single weight to drive both the timekeeping and striking mechanisms. Some 30-hour clocks were made with false keyholes, for customers who wished that guests to their home would think that the household was able to afford the more expensive eight-day clock. All modern striking longcase clocks have eight-day movements. Most longcase clocks are cable-driven, meaning that the weights are suspended by cables. If the cable was attached directly to the weight, the load would cause rotation and untwist the cable strands, so the cable wraps around a pulley mounted to the top of each weight. The mechanical advantage of this arrangement also doubles the running time allowed by a given weight drop._NEWLINE_Cable clocks are wound by inserting a special crank (called a "key") into holes in the clock\'s face and turning it. Others, however, are chain-driven, meaning that the weights are suspended by chains that wrap around gears in the clock\'s mechanism, with the other end of the chain hanging down next to the weight. To wind a chain-driven longcase clock, one pulls on the end of each chain, lifting the weights until the weights come up to just under the clock\'s face.'