Anyone knows please reply?

Please add your code as well

class LostTimeDetails(models.Model):

_name = 'lost.time.details'

_description = "Lost Time Details"

odometer_id = fields.Many2one('production.odometer', 'Production Odometer')

lost_time = fields.Char('Lost Time Activity')

start_time = fields.Float('Start Time')

end_time = fields.Float('End Time')

<field name="lost_time_ids" nolabel="1" attrs="{'readonly': [('state', '=', 'confirm')]}">

<tree editable="bottom">

<field name="lost_time"/>

<field name="start_time" widget="float_time"/>

<field name="end_time" widget="float_time"/>

</tree>

</field>

function for subtracting float_time fields:

@api.multi

def calc_button(self):

lost_time = 0.0

for line in self.lost_time_ids:

lost_time += line.end_time - line.start_time

line.lost_time = str(lost_time)

return