scale / digital scale
my surgeon uses Tanita brand but it does the print-out thingy to track your progress.... not sure if that's available in mass-markets but I got my Tanita scale at Bed, Bath, & Beyond for around $30 and it can track % body fat too. I've had it for a few years with no problems.
First ultra: Stone Mill 50 miler 11/15/14 13:44:38, First Full Marathon: Marine Corps 10/27/13 4:57:11, Half Marathon PR 2:04:43 at Shamrock VA Beach Half-Marathon, 12/2/12 First Half-Marathon 2:32:47, 5K PR Run Under the Lights 5K 27:23 on 11/23/13, 10K PR 52:53 Pike's Peek 10K 4/21/13, (1st timed run) Accumen 8K 51:09 10/14/12.