PS
# SampleFlow.m4
darrow_init

boxwid = 1.15
boxht = 0.6
linethick = 1.2

define(`dlthick',0.125)
define(`dfillcolor',`0.7,0.7,0.7')

define rbox {box rad boxht/10}
define offset { with .nw at last box.se+(-0.15,-0.125)}
define indent { at last box.w+(0.1,0)}
define connect {
 { Dline(from 2nd last box.s to (2nd last box,last box),E;ends=!-)
   dleft
   darrow(to last box.w) } }

command "{\sf"

B1: rbox
 { "Sample" ljust indent "Acquisition" ljust }
B2: rbox offset
 {"Sample" ljust indent "Checking" ljust }
 connect
B3: rbox offset
 {"Dimensionality" ljust at last box.w "Sample Check" ljust }
 connect
B4: rbox offset
 {"Sample" ljust indent "Synthesis" ljust "Techniques" ljust }
 connect

command "}%"
PE