Dynamic trend lines

Is there a command for calculating the value of a trend line in respect of two points in a data series? For example:

I want to know the current value of the trend line drawn between Low of third last bar and Low of the second last bar.

There is always the option of calculating the difference between the two Lows, then multiplying with the number of bars I want to look back.

if you know the name of the object then you just need to know the shift value:

double ObjectGetValueByShift(string name, int shift)The function calculates and returns the price value for the specified bar (shift related to the current bar). The price value is calculated by the first and second coordinates using a linear equation. Applied to trendlines and similar objects. To get the detailed error information, one has to call the GetLastError() function.
See also ObjectGetShiftByValue() function.
Parameters:
name - Object nameshift - Bar index.

Thanx a lot!