This simple Ruby script calculates HR Max based on formula created by Sally Edwards.

hr_max.rb

# calculates maximum heart rate for woman
# formula by sally edwards
def hr_max_woman(age, weight)
	return 210 - 0.5 * age - 0.022 * weight 
end

# calculates maximum heart rate for man
# formula by sally edwards
def hr_max_man(age, weight)
	return 210 - 0.5 * age - 0.022 * weight + 4
end

puts """
This simple script calculates HR Max (maximum heart rate) 
for woman & man based on formula prepared by Sally Edwards
"""

print "Type your age: " 
user_age = $stdin.gets.chomp.to_f

print "Type your weight: "
user_weight = $stdin.gets.chomp.to_f

man_hr_max = hr_max_man(user_age, user_weight)
woman_hr_max = hr_max_woman(user_age, user_weight)

puts """
If You're a woman, then Your HR Max is #{woman_hr_max}.
If Your're a man, then Your HR Max is #{man_hr_max}.
"""

# Links:
# * http://bieganie.pl/?show=1&cat=15&id=411