Corona SDK Orbiting object change direction - physics

Question

I have the following code:
deg = 0.0;
local function onTouch(event)
if(event.yStart >= event.y) then
deg = deg + 10;
elseif(event.yStart <= event.y) then
deg = deg -10;
end
rads = deg * (math.pi /180.0);
x = 100.0 * math.cos(rads);
y = 100.0 * math.sin(rads);
rect.x = magnet.x + x;
rect.y = magnet.y + y;
end
It in a way works, but it does not work perfectly. What I am trying to do is when the user drags up the object will rotate clockwise. when the user drags down, the object rotates counter-clock wise (by rotate I mean orbits another object).
The issue I am having is that deg keeps incrementing up/down when the user drags up or down. so when changing directions it will have to increment all the way down to 0 effectively to change directions. I can not figure out how to affectively reset variable deg without screwing the position of the object.
Thank ahead of time.
EDIT
After looking at the code Ive come to realize that the problem is NOT what i have stated above. The issue is that when i change direction the event.yStart does not reset!
so what happens, assume I start 200px, when i drag up the will increment up as long as i stay above 200px (whether i drag up or down. And wont start decrementing until I go below 200px.

Answer 1

deg = 0.0;
prevY = 0;
local function onTouch(event)
if event.phase == "began" then
prevY = event.y
end
if(event.y >= prevY) then
deg = deg + 10;
elseif(event.y <= prevY) then
deg = deg -10;
end
prevY = event.y
rads = deg * (math.pi /180.0);
x = 100.0 * math.cos(rads);
y = 100.0 * math.sin(rads);
rect.x = magnet.x + x;
rect.y = magnet.y + y;
end

Answer 2

You can try this:
deg = 0.0;
local prevPosY = 0
local function onTouch(event)
if event.phase == "began" then
prevPosY = event.y
end
if(event.y >= prevPosY) then
deg = deg + 10;
elseif(event.y <= prevPosY) then
deg = deg -10;
end
prevPosY = event.y
rads = deg * (math.pi /180.0);
x = 100.0 * math.cos(rads);
y = 100.0 * math.sin(rads);
rect.x = magnet.x + x;
rect.y = magnet.y + y;
end