The major and his staff will use a whistle of distinctive tone; the captain and company musicians a second and distinctive whistle; the platoon leaders and guides a third distinctive whistle. (_C.I.D.R., No. 15._) 35. Prescribed signals are limited to such as are essential as a substitute for the voice under conditions which render the voice inadequate. Before or during an engagement special signals may be agreed upon to facilitate the solution of such special difficulties as the particular situation is likely to develop, but it must be remembered that simplicity and certainty are indispensable qualities of a signal. _Orders._ 36. In these regulations an _order_ embraces instructions or directions given orally or in writing in terms suited to the particular occasion and not prescribed herein. _Orders_ are employed only when the _commands_ prescribed herein do not sufficiently indicate the will of the commander. Orders are more fully described in paragraphs 378 to 383, inclusive. _Commands._ 37. In these regulations a _command_ is the will of the commander expressed in the phraseology prescribed herein. 38. There are two kinds of commands: The _preparatory_ command, such as _forward_, indicates the movement that is to be executed. The command of _execution_, such as _MARCH_, _HALT_, or _ARMS_, causes the execution. _Preparatory_ commands are distinguished by _italics_, those of _execution_ by _CAPITALS_. Where it is not mentioned in the text who gives the commands prescribed, they are to be given by the commander of the unit concerned. The _preparatory_ command should be given at such an interval of time before the command of _execution_ as to admit of being properly understood: the command of _execution_ should be given at the instant the movement is to commence. The tone of command is animated, distinct, and of a loudness proportioned to the number of men for whom it is intended. Each _preparatory_ command is enunciated distinctly, with a rising inflection at the end, and in such manner that the command of _execution_ may be more energetic. The command of _execution_ is firm in tone and brief. 39. Majors and commanders of units larger than a battalion repeat such commands of their superiors as are to be executed by their units, facing their units for that purpose. The battalion is the largest unit that executes a movement at the command of execution of its commander. 40. When giving commands to troops it is usually best to face toward them. Indifference in giving commands must be avoided as it leads to laxity in execution. Commands should be given with spirit at all times. _Bugle Signals._ 41. The authorized bugle signals are published in Part V of these regulations. The following bugle signals may be used off the battle field, when not likely to convey information to the enemy: _Attention:_ Troops are brought to attention. _Attention to orders:_ Troops fix their attention.