Participants were requested to wear an actiwatch during the two weeks prior to a qualitative interview and to record their sleep in a structured sleep diary during that same period . An actiwatch is a small , wrist worn , device which measures movement on a minute - by - minute basis . It has been used widely within clinical sleep research as a proxy measure of sleep / wake ( Martin and Hakim , 2011 ) and has been shown to be suitable ( Sadeh , 2011 ) for identifying rhythms . The raw data from the actiwatch can be plotted to create a personalized actogram [ Fig . 1 ] . Each horizontal line in the actogram represents a 24 - h period ( from midnight to midnight ) . Black vertical lines represent movement , with the height of the line indicating intensity of movement . In a ' normal ' , monophasic pattern we would expect movement to be concentrated in the middle of each day with little movement to the far right and far left of each line . In Fig . 1 , which represents the total two - week period from a single participant , what is immediately of interest is ( i ) the constant and continuous movement across the 24h period and ( ii ) a lack of any clear demarcation between day / night movement . The actigraphy data were downloaded prior to the interviews and used during them to encourage participants to reflect on and interpret their personalized graph . The self - completion diaries ( when completed ) were also used during the interviews as prompts to recall and to help participants ' make sense ' of the actigraphy data . The actigraphs and diaries in effect acted as what Latour ( 1987 ) would call ' inscription devices ' ; encouraging a richer understanding of sleep as they provoked participants to reflect subjectively on seemingly objective measures of movement , rest and sleep .