- p7, L304-305: "99.9% efficiency when using OR of both chambers" and "azimuthal resolution of 300murad" are not simultaneously feasible, because for the angular resolution an AND of both chambers is implied.

- p7, L326-327: there should be no need for a "low material budget", because at high rapidity the expected muons have very high energy. What is relevant w.r.t. material budget is probably the emission of deltas, which tend to mask the muon hit. And here it is not obvious whether one should use thin or less thin materials.

- p.9-11: the Ar/CO2 70/30 (COMPASS) gas seems to be very suited for CMS. Which are its disadvantages i.e. why not use it for CMS, avoiding the complications and costs of other additives?

- p. 41, L870-872: please tell which is the electric field for the drift regions in the planned chambers (otherwise one cannot understand the statement, whenn looking at Fig. 2.6 in p. 10).

- p. 41, L874-880: these statements are invalidated by the fact that on a closed chamber one cannot see the GEM foils any more (remember: at closing a tiny deformation is not excluded, so it should be checked after closing). Furthermore, even on an open chamber one cannot see the three GEM foils but only the top one - the shape of the other ones is not necessarily the same and hence remains unknown. This because the method of tensioning cannot ensure the same tension to every foil, since it tensions the package of three foils, which are not elastic. The suggested "assure flatness and uniformity to about 30 mum" cannot hold. By the way, it is left open whether the check described should be done on the ref. chamber only, or on all chambers.

--> Alternative measurement methods, to be applicable on the closed chamber, should be studied.

- p. 42, L887 and Fig. 2.47: air being less dense than the gas mixture used, the gas inlet of each chamber should be at its lowest point to avoid pockets in case of some leak or any lighter gas. This is not said, nor suggested by the figure, where the inlet is shown at the top.

- p.43, L915: "5 mbar overpressure expected in GE1/1" means 25 kg over the surface (about 0.5 m**2) of the two PCBs serving as enclosure. Is their deformation, at the center, not going to be too large for the flatness specs given on p. 41?

- Chapters 4 and 5: no external referencing for the readout electrodes foreseen? The hardware alignment described in a later chapter seems not to exist, here. The many (>3k) electrodes of the readout-PCB are not visible from outside; furthermore this PCB is hidden under the "GEB" PCB and under an Aluminum cover. As described in this chapter, no hardware alignment is possible. Note: at no cost a precise referencing (copper marks on the outer PCB face, holes) can be included in the PCB production, permitting to implement a referencing on the closed chamber.

- p. 70, L.1494 vs. p. 71, L1571: two different clean room classes required (1000, then 100).

- p. 72, L1598-1603: the stretching step is of central importance, but not mentioned in the list...

- p. 72: the flatness check of the stretched GEM foils is not mentioned here, for the mass production. Will there be no check?

- p.73, L1631: which resolution is required? Are absolute positions part of this test? (...but there is no mention of any referencing)

- Chapter 5: many steps listed, but (a) foil flatness and (b) alignment referencing seem to be fully ignored.

Entered by M. Hohlmann for Hans

-- MarcusHohlmann - 2014-12-16