Altimeter, Model: 4FGH 40, 20,000 feet, inHg, 3-pointer - Popular
This altimeter is very popular with glider pilots because of its small size. It fits nicely into the small instrument panels found in many sailplanes. It is the only small (57 mm) altimeter for use in a certificated airplane that I am aware of.  However, there may be some compromises due to its small size.  Some pilots find it more difficult to read than other (larger) altimeters.  It seems obvious to me, that the small size would make it more difficult to read, but I have flown with them and I had no problem reading it.  In 2007 Winter changed the 3rd pointer from a short white pointer to a long, thin black pointer with a red colored tip (see photo at right).  That should make the unit easier to interpret in flight. 

Also, the accuracy appears to be less than that of other (larger) altimeters. The Manual and Specifications indicate that the altitude error may be as much as +/- 120 feet at 8000 feet - more at higher altitudes.  That doesn't concern or surprise me, but it is good to be aware of it.

Size: 57 mm (2 1/4"), Range: 0 to 1,000 to 20,000 feet, Inch (Hg) pressure scale, zero at 12 o'clock
3-pointer altimeter for measuring absolute and relative altitudes in the 0 to 20,000 ft range.
Indicating Range: 0 to 1000 to 20,000 feet.

Note: The W-4555 altimeter is calibrated up to 20,000 feet, but will indicate up to about 26,000 feet (~8,000 m). It will not be damaged if you go higher than that. 

Scale graduation: large pointer: 10 feet per line, small pointer: 100 feet per line, third pointer: 1000 feet per line
Pointer Travel, Long White Pointer: 1,000 ft/rev, Short White Pointer: 10,000 ft/rev, Red-tipped Pointer: 100,000 ft/rev
Technical Data
Airtight, black plastic housing.  Connection via hose from static pressure sensor to hose connector at the rear.  Kollsman window with scale in inches of Hg.  See scale drawing at right for installation dimensions.  Weight: 0.235 kg (8.3 oz).  360° linear scale.  This altimeter can be fitted with a W-4022 scale ring.
Manual and Specifications 
Leakage Test 
Adjusting an Offset in the Subscale