old_contents: # log the accelerometer values to a .csv-file on the SD-card
  
  import pyb
  
  accel = pyb.Accel()                                 # create object of accelerometer
  blue = pyb.LED(4)                                   # create object of blue LED
  
  log = open('1:/log.csv', 'w')                       # open file to write data - 1:/ ist the SD-card, 0:/ the internal memory
  blue.on()                                           # turn on blue LED
  
  for i in range(100):                                # do 100 times (if the board is connected via USB, you can't write longer because the PC tries to open the filesystem which messes up your file.)
          t = pyb.millis()                            # get time since reset
          x, y, z = accel.filtered_xyz()              # get acceleration data
          log.write('{},{},{},{}\n'.format(t,x,y,z))  # write data to file
  
  log.close()                                         # close file
  blue.off()                                          # turn off LED
  
new_contents: # log the accelerometer values to a .csv-file on the SD-card
  
  import pyb
  
  accel = pyb.Accel()                                 # create object of accelerometer
  blue = pyb.LED(4)                                   # create object of blue LED
  
  log = open('/sd/log.csv', 'w')                      # open file to write data - /sd/ is the SD-card, /flash/ the internal memory
  blue.on()                                           # turn on blue LED
  
  for i in range(100):                                # do 100 times (if the board is connected via USB, you can't write longer because the PC tries to open the filesystem which messes up your file.)
          t = pyb.millis()                            # get time since reset
          x, y, z = accel.filtered_xyz()              # get acceleration data
          log.write('{},{},{},{}\n'.format(t,x,y,z))  # write data to file
  
  log.close()                                         # close file
  blue.off()                                          # turn off LED
  
subject: Change 1: to /sd/, and update comment about FS.