I don't know who compiled this, but it makes an interesting checklist.
No doubt others can be added in replies. There are some duplications.
Things That Can Make A Clock Run Slow1. Pendulum bob too low.
2. Suspension spring too long.
3 Plates warped / bent, squeezing the pivots.
4 No lubrication
5 Gummed-up lubrication
6 Weak or "set" mainspring
7 Dried or gummy lube inside hour cannon
8 Pendulum bob too heavy, causing C.O.G. to be too low
9 Anything that can increase the effective length of the pendulum will reduce the rate of the pendulum, making the clock run slower.,
10 forgot to wind the clock,
11 mechanical alterations like changing the escape wheel,
12 slipping clutch, and
13 cracked pinion.
14 Absentmindedness - that is the clock was incorrectly set to begin, which admittedly won't make the clock run slow but just make it seem that way.
15 Moving a clock to a higher elevation will make it run slow, as the gravity is less and the air is thinner.
16 Increasing the ambient temperature a clock is in will slow it down, from the expansion and lengthening of the pendulum rod(unless it's a compensating type).
17 A loose clutch will make a clock "appear" to run slow, if the clutch sometimes slips.
18 With a recoil escapement clock, general loss of power, whether from weak mainspring or frictional losses(lack of lubrication, wear, etc.) will cause the clock to run slow.
19 increase the swing so much that circular error becomes a factor.
20 suspension spring (at the top of where the pendulum bob hangs) is not attached correctly
21 Sometimes clocks that have been stored end up with their pendulum bobs getting lost or mixed up with others.
22 the most likely cause of a clock running slow is usually a physical issue with the pendulum system unless someone has grossly altered the movement
23 If it is losing hours a day, it is most likely something slipping.
24 If it is a few minutes a day is could just need bushings.