Jim, the problem with distributor timing fixtures/tools is that so often the user does not understand how the distributor works ... not saying you, but usually.
The instructions on the device explain its operation. However, if you know what you are trying to do, you wouldn't need instructions at all. For example, hammers do not come with instructions ... but if they did, they'd be 3 pages long.
For the Tasco, set both sets of points at .014. Set the pointer on an 8 mark. Move the sliding index on the side of the distributor until the light just goes out. That is the LH points opening and firing the plug.
This sets the dwell and the initial advance. They give the additional step of the light coming back on within the white block. That confirms that the RH points are closing and initiating the proper dwell period which means the light stays lit until the next 8 mark. If the light comes on outside the block, fiddle with the RH points until it does. (RH/LH is as distributor installed viewed from sitting in the front seat.)
Worst instructions are the KR Wilson ... they take 3 steps and condense them into 47. Don't need no stinking instructions.
Really simple stuff that is treated like alchemy.