The following data pertains to the month of October for ElmCo - when production was budgeted to be 5,000 units of P90. P90 has standard costs per unit of:

3 lbs. of Direct Materials at a cost of $7.00 per lb

0.20 hours of Direct Labor at $18.00 per hour

Variable Overhead assigned on the basis of 0.05 machine hours at a rate of $50 per machine hour.

In October the actual production of P90 totaled 4,600 units, using 324 machine hours costing a total of $17,066.

Determine the variable overhead efficiency variance. (Negative numbers indicate a favorable variance.)