why we need both vel and acc contribution for actual position?

I was trying to understand multiwii quadcopter code. I started with understanding GPS code. Here is a section of the code where I have doubt. Why actual position = pos + velocity contribution + acceleration contribution ? I mean velocity contribution and acceleration contribution, both are the same thing (I Think). So what is the purpose of adding both vel contribution and acceleration contribution ?

Here is the section of the code:

class LeadFilter { public: LeadFilter() : _last_velocity(0) { } // setup min and max radio values in CLI int32_t get_position(int32_t pos, int16_t vel, float lag_in_seconds = 1.0); void clear() { _last_velocity = 0; } private: int16_t _last_velocity; }; int32_t LeadFilter::get_position(int32_t pos, int16_t vel, float lag_in_seconds) { int16_t accel_contribution = (vel - _last_velocity) * lag_in_seconds * lag_in_seconds; int16_t vel_contribution = vel * lag_in_seconds; // store velocity for next iteration _last_velocity = vel; return pos + vel_contribution + accel_contribution; }