brass vs. iron

[Newton Hunt]

You said the hall has cool earlier then heated up before the audience
was let in.

Since the piano was covered until just before concert time, and with the
change in termerature I think the humidity changed enough to effect the
tune.

Low tension instruments are effected two or three time more and far more
quickly  by changes in humidity than high tension instruments.

This is a situation of "must have".

The hall must be stable at the same temperature AND humidity two to
three hours before tuning and before performing.

                Newton