At a meeting of the Change Control Board this morning, the subject of stability, not on the agenda, arose. Massimo announced his intention to take a decision. Recall the Charge the Board gave the ASAC: "It is technically very challenging to achieve the current amplitude calibration goals (1%/3% below/above 300GHz), and the specifications on total power stability (currently 10-4 over 1 second, 3×10-3 over 5 minutes, 5×10-4 over 5 minutes on the differential gain of two polarisations), specifications which can have significant impact on cost and schedule." The ASAC report delivered to the Board on 4 November 2003, stated, in part: "In particular, to measure polarisation accurately in interferometric mode to 0.1% levels requires a differential gain stability between the two polarisation channels of better than 5×10-4 in 5 minutes, the typical time betweenwhich calibration of instrumental polarisation can be performed. This specification has been deleted from the most recent proposed specifications. Without such a specification, the ability of ALMA to measure polarisation accurately may be lost. The ASAC believe it is necessary to (1) re-introduce a specification on differential gain between polarisations; (2) make the appropriate measurements of differential gain stability between the two polarisation channels on a representative receiver prototype; and (3) conduct detailed simulations which allow the effect of receiver stability on polarisation measurements to be quantified." At the CCB we reviewed the results of the stability telecon last week, for which my report reads: "Charles and Gie Han asked that we concentrate on providing specifications which would allow them to finish the contracts. On phase stability, we decided that it was up to the SE group to tell the FE group what their budget was. We agreed on 10 fs. Larry will write a memo making this draft assignment and place it on almaedm so that it might be referred to specifically in contracts. On gain stability, attention focussed on Larry's note of 14 July, in which he proposed a standard for gain stability measurements. The graph at the end of that document was proposed to be the spec (it is based on noise alone; no atmosphere is included). It was placed on almaedm. The spec in that document is somewhat better than what the ASAC had called for. Again, this is a draft spec. We decided that when Mark Holdaway's simulations which include the atmosphere are published, the draft spec will be changed to reflect the atmosphere. The FE Group was happy to have project specifications; I think all involved were satisfied with the phase specification. As we know, the gain spec may be hard to achieve in practice. We decided that managing that is a problem for the FE group, management, and business (or whoever writes the contracts). After two hours of discussion, we adjourned when people from the next scheduled telecon began to phone in. I don't consider the discussion finished, but I think it was constructive." The discussion certainly wasn't finished then. Massimo noted that this was a goal but not a spec for the receiver contract. We had some discussion. I said that good science could be done with numbers similar to those in the measurements of B6 made by the CDL group and that 4 x 10-4 s-1 stability would not limit the science drastically. MT noted: This applies to the total power antennas. For any given receiver, it cannot be worse than 10-3. On the total power antennas, stability must be at least 4 10-4 s-1 total. Sramek noted: SE allocation of 1e-3 s-1: 7 e-4 s-1 to front end and same to back end. Out of 80 we need four receiver packages which meet this spec; they may be selected. Those selected cartridge elements then are shipped to Japan, should Japan join, where they are integrated into the packages for the total power frontends. I noted that good polarization measurements required 5 x 10-4 s-1 over five minutes as in the original draft specification. I don't think that either the Science IPT or the Front End IPT are entirely happy with this decision. However, we all will be happy to see receiver contracts written. In the FE report to the JAO IPT meeting of 24 November it was reported: "Intensive discussions with the SE&I IPT have been held to resolve the outstanding spec items for the FE assembly and FE cartridges. With input from the Science IPT it was agreed with the JAO that for the front-end an amplitude stability of 7.10-4 at 1 sec timescale shall be achieved. The total ALMA amplitude stability shall be better than 10-3 at 1 sec timescale." In the CCB minutes this was reported as: (see http://almaedm.tuc.nrao.edu/forums/alma/dispatch.cgi/ccbmeet/docProfile/100029/d20031119211028/No/t100029.htm) Amplitude Stability Requirement Following Amplitude Stability Requirement for the ALMA system was agreed: 10 -3 for all ALMA 12m integrated antennas 4 10-4 for the four ALMA 12 m antennas used for total power measurements The system requirement document needs to be updated accordingly.